Of course, the very phrase "collapse of the civilization of the Ancients" conjures a circumstance that exists in *our* minds, not in the minds of the people to whom it "really happened". True, the Last One does as it were eulogize the destruction of what he calls The Perpetrated World, but this Author is so susceptible to exaggeration and rant that it is difficult to know when he is being literal and when metaphorical (or merely sarcastic) in his utterance. The almost banal experience he describes — "Suddenly one day, nothing worked, and then everyone disappeared" — was no doubt shared by other survivors, whereas the people most directly affected by this "collapse" may well have been annihilated in an instant.
However these latter souls met their demise, they left no record behind. So we may as well accept the fact that we will never know "what really happened". Our story of their story can only be made up of those materials from which a story can be made up.