I was thinking about the fact that for multiple generations Roman citizens could have thought that the empire was never going to end. But did those who were living in the end times of the reign indicate in any way that they thought this was it (kind of like some people today in the US) or did they carry on thinking we'll make it through this?
While not directly answering your question, this answer from the askhistorians FAQ gives context on the fall of the Western Roman empire by u/iguana_on_a_stick (With the Eastern Roman empire not ending till the fall of Constantinople in 1453 and even then the Ottomans kept the roman empire as part of its titles till it was overthrown in 1922!!)