The other ancient superpowers will be china in the east. Like Rome, it has been split and conquered many times. Yet somehow the infrastructe of the chinese government surive till this day.
Arguably China is a more geographically natural unit, Persia also. I think it would be hard to argue that they have significantly more continuity than Western Europe does from the Roman Empire, extensive use is still made of Roman legal concepts, language and to an extent philosophy.
This is simply not true, the Romans never ran out of manpower. They ran out of land and money and properly trained and equipped men.battles, but by throwing legion and legion at enemies while losing battles, because they "always" had more reserves. At least until they really needed them. It's a mistake to consider the residents of the formerly western Roman lands the descendants of the Romans. The barbarian invaders didn't assimilate into Roman culture, firstly, and they replaced the Romans (although the Goths did keep some Roman infrastructure intact). The inhabitants of Italy aren't Romans; they're Germanic Lombards with a bit of an Arab twist.
Aside from the fact that the population of the Empire would not have been "roman" in any ethnic sense it is quite clear that the Romans did integrate with the invaders, landowners would usually lose about 1/3-1/2 their land to barbarian leaders and gradually a merged ruling elite emerged