When the Roman Empire fell there were two distinguishing characteristics:

1) It didn't happen overnight, or everywhere; it took centuries, and it happened in one area at a time.

2) The social structure that took over was feudal--local warlords and "aristocrats" supported by bands of armed men, relying on an agricultural peasant class to grow the food. It is interesting to note that slavery really didn't catch on, even though it had been the dominant form of production during the Empire.

This pattern has repeated itself all over after an Imperial collapse; Warlord China, Samurai Japan, Chivalric Europe, the pre-Inca Andean kingdoms and the Eastern Med after the fall of Mycenae. (For a great insight into that period, read the Odyssey. Odysseus was called King of Ithaca, but he was really just a vassal landowner with barely the ability to assemble a force of 12 ships and 600 men to fight in his leige lord's war at Troy).

The seeds of feudal aristocracies and their men-at-arms exist today; crime gangs, the Mafia, biker clubs, survivalists and militias. The only thing we lack today is a peasantry that knows how to farm using animal-powered plows.

As for the seedy nature of these proto-feudal organizations, what makes you think they are any more disreputable than the armored, horse-riding bullies of the so-called Lords and Ladies of the Age of Chivalry?

Still I agree with you. A modern civilization can probably absorb a lot more punishment than we think it can before it finally caves in. Look how long Nazi Germany was able to hold together in the face of complete encirclement by its enemies, and constant aerial bombardment. And even the corrupt and top heavy Soviet Union was able to transition successfully with relatively little violence and confusion.