Diocletian's reforms were probably forced by necessity and the western part of the empire continued to exist and even thrive a long time after Diocletian was dead. We would not pin the Cold War on Napoleonic reforms either.
The foederati system does not seem as bad as Bret Devereaux puts it. It is not that different from modern NATO and a ton of other, earlier alliances among sovereigns. And a lot of Germanic people actually integrated into late Roman society, including a famous general named Stilicho, who was of Vandal origin.
The invasion of the Huns was pretty traumatic for the Western Roman Empire and it is possible that if it did not happen, or if the Huns met defeat early, the empire could have limped along for next thousand years, just like the Eastern Empire did.
In studying defeats and collapses, we tend to overlook other instances of similar problems that did not end up catastrophically.
Austria, and later Austria-Hungary, a hodgepodge of nations of unequal standing, was able to survive for many centuries before disintegrating in 1918 because it lost a major war so thoroughly that the civilian population was struck by long famine.