I think it depends a lot on how you define "collapse".
I'm doubtful of the wheelbarrows of money scenario.
However I think we're eventually going to see a revaluation of the dollar vs asian currencies that is going to make for a significant quality of life hit.
Also I think we might match some of the historical highs for inflation and experience 10-20% inflation per year for a while.
So if dropping to a third of its purchasing power over a span of five years is a "collapse" I think we'll see it within the next decade or so.