[przeor]

How come, maybe they just stop printing new dollars when the govt collapse?

USD can exsist without govt. It can't exsist without army behind the paper , at least on paper.

[kolinko]

There were multiple cases in history when governments failed, I think their currencies never survived this. Hyperinflation in such situations tends to devalue money so much that it's not worth the paper it's printed on.