[sumsome]

> TL; DR Difficult after ~2.5 million years unless they had a nuclear war

Scary if they didn't!

EDIT: what else killed them off or where did they go and will they come back, so it's actually quite curious and less scary but it made me shiver when I read it the first time.

[lazide]

Eh, plagues or evolutionary ‘black holes’ followed by an outside context problem are all possible too. Aka Dodo bird type situation.