So, how're we gonna approach this? Here's my proposal for how we go about it:
If the Huns focus on the Eastern Empire, its not unrealistic to imagine them as allies of the west (they were often allies anyway). This could help the West hold on to their territory, assuming both sides honor their agreement. The Hunnic empire would keep the barbarians in line, mainly by getting everyone they ruled to gang up on Byzantium, while ganging up with Rome against the other tribes (like the Visigoths). I figure many of the tribes will start settling in Byzantine territory, to get away from the Huns.
For this to happen, we would need some effective leadership on both the part of Rome and the Huns. We could easily find it in General Aetius and Attila, both who died before their time (and who both happened to be friends). Avoid the debacle with Honora, and Attila leaves the West alone. Smooth things out between Aetius and Emperor Valentinian, and keep Attila from dying in his sleep.
Or, have Valentinian marry Honora to Attila. He actually had his other sister, Placidia, marry a Vandal prince, so this would be within the realm of plausibility.
Either way, if Aetius stays around (we could even make him Emperor, if we wanted), the West will fare much better. He's the kind of guy who could hold things together. It'd be even easier with the Huns on his side.
So, what do you guys think we should go with? Just have the Huns allied, or should we marry Honora and Attila? If they get hitched, the Huns could prove to be more valuable and loyal allies, but, there's the possibility of court intrigues messing stuff up. Which would be ironic, as thats the kind of stuff you'd expect from Byzantium.
Or, of course, we go with one of the other ideas, I'm just throwing out ideas for you guys.