Firstly, I would like to say I have a TL on this topic (check the sig) with a POD no Camillus saving Rome from the Senones, therefore there is a successful Senone destruction of Rome under Brennus. An unstable Senone kingdom is established in central Italy that for a few years expands throughout Etruria and Latium by sheer military momentum, but shit hits the fan. 
Ok,so long term *cracks knuckles*
I think Carthage would be a regional power in the western med sea for a while, but the Numidians would probably overcome them in the long run, at least in Algeria. Southern Spain was thoroughly Punicized, so I think unless some kind of genocide occurs, we can see Punic off-shoot languages in Spain (Ishfania) as well as North Africa, Malta, and the Balearic Islands. I would say one of these Punic successors would be the ones who discover the Americas, probably by ~900 A.D. (or what would equate to it).
As for the Greek world... well, its very very tricky. Things can go so many ways with all the wars between Diadochi, and then when the Galatians invade, AND THEN when the Parthians invade... There's a lot to take account for. I think, without any sub-POD's, you would most likely see Macedonia reunify Greece (it was a Roman priority to see that this never happened). Pyrrhus of Epirus would probably create a short lived and unified Epirote controlled Magna Graecia and Sicily, ousting the Carthaginians from Sicily like OTL, and able to retain control of said areas without Roman intervention. From there what happens is anyone's guess, but it would be fair to say a Greek majority would likely remain in Sicily and Magna Graecia until modern times, perhaps creating different languages along the way that branch off from main-line Greek.
I honestly think that the Seleucids are screwed if nothing changes before Antiochus III. The Parthians come along and invade Persia, the Jews gain independence, and the Armenians seize control of Syria and eastern Anatolia. Maybe the Armenians can hold Syria, and even take control of Palestine, who knows?
Dacia would likely unify under Burobista in the 1st century B.C. The Dacians oust the Celts from the Carpathians, and push into parts of Germany. This kingdom, however, will be unstable, and while it would be a huge threat to the Greeks, I think it would collapse in the wake of Germanic and Sarmatian migrations into the area. However, some form of Dacian might still be spoken in the mountains in modern times, best case scenario.
Egypt would probably decay under Ptolemy rule, eventually succumbing to revolt in which a short-lived native Pharaoh rules, but is overtaken by whoever the strongest power in the east med. sea is, because Egypt is just too valuable not to have. So could fall to either Seleucids, Armenians, Macedonians, Parthians, or Carthaginians depending on time period and your fancy.
Iberia, like I said, will be Punicized in the south, but will likely remain Celtic in the North. The Lucitanians were on the decline, and will be completely absorbed into Celtic culture. I'm unsure how long it will take for unified states to pop up, ancient Iberia is one of the chinks in my intellectual armor
GAUL!!!! CELTICA!!!! oh baby, my favorite. Well, as someone mentioned earlier, the Sweboz did invade Gaul, making the Sequani their bitch, by the time Julius Caesar walked in. However, what they failed to mention is that at this point in time the Romans had already taken over and invaded Gaul Narbonensis, southern Gaul, defeating the Allobroges (because they decided to invade Massalia, who was a Roman ally) who were close allies to the Arverni and Sequani, and would have been quite the help against the Sweboz. Not to mention the Arverni would still have been the most powerful hegemon without Roman intervention, meaning more Arverni to kick Germanic ass. In other words, the Sweboz would likely invade during and after the Arverni-Sequani-Allobroge alliance defeated the Aedui and their allies. The A-S-A alliance would then oust the Sweboz, pushing them back across the Rhine, where they belong. The Helvetti would relocate without the big fuss Caesar made, probably moving into Aquitainia. The most likely group to unify Gaul would be the Arverni with their capital in Gergovia.
I think the Gaulish language would adopt Greek letters for their alphabet eventually, which would trickle over to Britain, and so on. Interesting things would happen in Britain. Without Roman conquest, the Belgae tribes will not migrate there, meaning much of Southern Britain will be different. No Icene (meaning no Boudicca), no Belgae, no Dumnoni, none of that. It's hard to say what will happen there, but I think it would likely remain a backwater for a very very long time, undergoing invasions from Gaels, Scandinavians, and Picts who are arguably non-Celtic, or even non-Indo-European. In otherwords, chaos. They would be lucky if a unified Gaul decided to invade, perhaps to end piracy.
Germanic tribes would make a big mess of things. However, without Roman slaughter of the Celts, they would have a slightly lesser influence in Germania. Instead, many would move towards the Black Sea (like OTL, maybe a bit more) and there will be the center of Germanic culture. The void left by Germanic migrations will probably be filled by Slavs, like OTL, only instead of moving into the Balkans, they will move into the less profitable, less populated, less defensible, and less cultivated Germania. I'd say modern day Bohemia, Bavaria, and Austria would all either be Celtic, Slavic, or maybe mixed.
Illyria I think will either be Celticized or Hellenized. Maybe both, depending on how North or South. I doubt Illyrian piracy would be much tolerated as time passes.
Italy will be a cluster-fuck backwater shitheap without the Romans. Samnites running around, Celts in the north, Etruscans in Tuscany, Sabines and other Umbrians in central Italy, and Greeks in the South. I doubt any real unification would come for a very long time. Whats more likely is that, as time passes, Italy develops into 3 regions. North, dominated by the Celts, South, dominated by the Greeks, and central which I'd put money on the Samnites to dominate.
Religion will be more loosy goosy. I think the Cult of Isis would gain a lot of popularity throughout the mediterranean world, as could the cult of ba'al. Zoroastrianism persists in Persia, and might be the catalyst for a Christian analog.
However, I think Buddhism would be more interesting. If the Seleucids and the Greco-Bactrians can last longer, Buddhism might gain a foothold in the Greek world.
Judaism would undoubtably have offshoots bearing similarity to Christianity, but it is uncertain if any will have great appeal. One, if it came out, would likely be popular in places like Egypt, which had a large Jewish population, and Carthage, which had a large Semitic population.
Ok,so long term *cracks knuckles*
I think Carthage would be a regional power in the western med sea for a while, but the Numidians would probably overcome them in the long run, at least in Algeria. Southern Spain was thoroughly Punicized, so I think unless some kind of genocide occurs, we can see Punic off-shoot languages in Spain (Ishfania) as well as North Africa, Malta, and the Balearic Islands. I would say one of these Punic successors would be the ones who discover the Americas, probably by ~900 A.D. (or what would equate to it).
As for the Greek world... well, its very very tricky. Things can go so many ways with all the wars between Diadochi, and then when the Galatians invade, AND THEN when the Parthians invade... There's a lot to take account for. I think, without any sub-POD's, you would most likely see Macedonia reunify Greece (it was a Roman priority to see that this never happened). Pyrrhus of Epirus would probably create a short lived and unified Epirote controlled Magna Graecia and Sicily, ousting the Carthaginians from Sicily like OTL, and able to retain control of said areas without Roman intervention. From there what happens is anyone's guess, but it would be fair to say a Greek majority would likely remain in Sicily and Magna Graecia until modern times, perhaps creating different languages along the way that branch off from main-line Greek.
I honestly think that the Seleucids are screwed if nothing changes before Antiochus III. The Parthians come along and invade Persia, the Jews gain independence, and the Armenians seize control of Syria and eastern Anatolia. Maybe the Armenians can hold Syria, and even take control of Palestine, who knows?
Dacia would likely unify under Burobista in the 1st century B.C. The Dacians oust the Celts from the Carpathians, and push into parts of Germany. This kingdom, however, will be unstable, and while it would be a huge threat to the Greeks, I think it would collapse in the wake of Germanic and Sarmatian migrations into the area. However, some form of Dacian might still be spoken in the mountains in modern times, best case scenario.
Egypt would probably decay under Ptolemy rule, eventually succumbing to revolt in which a short-lived native Pharaoh rules, but is overtaken by whoever the strongest power in the east med. sea is, because Egypt is just too valuable not to have. So could fall to either Seleucids, Armenians, Macedonians, Parthians, or Carthaginians depending on time period and your fancy.
Iberia, like I said, will be Punicized in the south, but will likely remain Celtic in the North. The Lucitanians were on the decline, and will be completely absorbed into Celtic culture. I'm unsure how long it will take for unified states to pop up, ancient Iberia is one of the chinks in my intellectual armor
GAUL!!!! CELTICA!!!! oh baby, my favorite. Well, as someone mentioned earlier, the Sweboz did invade Gaul, making the Sequani their bitch, by the time Julius Caesar walked in. However, what they failed to mention is that at this point in time the Romans had already taken over and invaded Gaul Narbonensis, southern Gaul, defeating the Allobroges (because they decided to invade Massalia, who was a Roman ally) who were close allies to the Arverni and Sequani, and would have been quite the help against the Sweboz. Not to mention the Arverni would still have been the most powerful hegemon without Roman intervention, meaning more Arverni to kick Germanic ass. In other words, the Sweboz would likely invade during and after the Arverni-Sequani-Allobroge alliance defeated the Aedui and their allies. The A-S-A alliance would then oust the Sweboz, pushing them back across the Rhine, where they belong. The Helvetti would relocate without the big fuss Caesar made, probably moving into Aquitainia. The most likely group to unify Gaul would be the Arverni with their capital in Gergovia.
I think the Gaulish language would adopt Greek letters for their alphabet eventually, which would trickle over to Britain, and so on. Interesting things would happen in Britain. Without Roman conquest, the Belgae tribes will not migrate there, meaning much of Southern Britain will be different. No Icene (meaning no Boudicca), no Belgae, no Dumnoni, none of that. It's hard to say what will happen there, but I think it would likely remain a backwater for a very very long time, undergoing invasions from Gaels, Scandinavians, and Picts who are arguably non-Celtic, or even non-Indo-European. In otherwords, chaos. They would be lucky if a unified Gaul decided to invade, perhaps to end piracy.
Germanic tribes would make a big mess of things. However, without Roman slaughter of the Celts, they would have a slightly lesser influence in Germania. Instead, many would move towards the Black Sea (like OTL, maybe a bit more) and there will be the center of Germanic culture. The void left by Germanic migrations will probably be filled by Slavs, like OTL, only instead of moving into the Balkans, they will move into the less profitable, less populated, less defensible, and less cultivated Germania. I'd say modern day Bohemia, Bavaria, and Austria would all either be Celtic, Slavic, or maybe mixed.
Illyria I think will either be Celticized or Hellenized. Maybe both, depending on how North or South. I doubt Illyrian piracy would be much tolerated as time passes.
Italy will be a cluster-fuck backwater shitheap without the Romans. Samnites running around, Celts in the north, Etruscans in Tuscany, Sabines and other Umbrians in central Italy, and Greeks in the South. I doubt any real unification would come for a very long time. Whats more likely is that, as time passes, Italy develops into 3 regions. North, dominated by the Celts, South, dominated by the Greeks, and central which I'd put money on the Samnites to dominate.
Religion will be more loosy goosy. I think the Cult of Isis would gain a lot of popularity throughout the mediterranean world, as could the cult of ba'al. Zoroastrianism persists in Persia, and might be the catalyst for a Christian analog.
However, I think Buddhism would be more interesting. If the Seleucids and the Greco-Bactrians can last longer, Buddhism might gain a foothold in the Greek world.
Judaism would undoubtably have offshoots bearing similarity to Christianity, but it is uncertain if any will have great appeal. One, if it came out, would likely be popular in places like Egypt, which had a large Jewish population, and Carthage, which had a large Semitic population.
