Philip the Great of Macedon

What if Philip II of Macedon wasn't assassinated by his bodyguard/lover on the eve of the invasion of Persia? I think it was highly likely he would succeed conquering Persia. The Macedonian army was built by Philip and a man as intelligent and experienced as Philip would hardly fail in this campaign. Alexander himself would still serve his father as a frontline commander rather than the soverign.

In my view Alexander was a colossal failure in many ways. He's problem was his youth. He was too young to just stop with the conquest of Persia. Instead of consolidating his empire he kept expanding until his death, which resulted in a very short lived Macedonian empire. It's possible Alexander had to keep campaigning because he lacked the political strength to command his empire as anything other than a military leader.

OTOH Philip was in his late forties when he was killed. Conquering Persia was his lifelong dream. There is no reason to suppose he would continue campaigning after Persia. A lasting empire could be the result. Such a Greco-Persian empire could stretch from Italy to India and last centuries. The vary concept of a divided East-West world would fade into obscurity.

Did he want all of Persia, or would he accept a peace offer giving him everything west of Euphrates?

Yes, after Darius had lost a battle - Issos, I think.

Acceptance of similar terms is very likely. Precisely because Philip was an intelligent, experienced warleader he was not used to thnking in world-spanning sweeps. He actually listened to his generals, for one thing. So the likely outcome is that he pushes his troops into a military vacuum in Asia Minor, registers with surprise how quickly the Persian West caves in, and decides to secure this completely unexpected bounty. Ofg course he knows that no peace offering by the Great King will be valid for longer than it takes the Persians to be in a position to strike back, but he plays by these rules himself.

so he wont accept
maybe if philip consolidates the empire alexander has a fitter empire to use for his campians after philip died. bigger army good administration in the capital etcetra... and because alexander is older he will expand on a better way then he did in OTL