Theory

[Alardem]

Who's to say that Mandus DIDN'T drastically change the course of history? The universe of Amnesia diverges from ours from the point Mandus had his vision of our 20th century, because of all his attempts to avert it lead to something even worse. Also, the Man-Pigs have one advantage of being nigh-invincible - the chemical that fuels their body is apparently potent enough to make severed heads come back to life. Finally, I got the impression that, in his dying moments, Mandus' link to the Machine allowed him to glimpse the surface.

It's a weird, vague story, and I do agree that the areas at the end are pretty abstract. But I don't think Pinchbeck is enough of a hack to cop out and say 'nothing happened'.

Spoiler below!

Or do what Ken Levine does and literally undo everything via killing Hitler.