It is not about the complete demise of the US empire. Rather, it is about a material reduction of the living standard for ordinary US citizens, and also a fundamental reduction of the US political and military power in shaping international economic and political development.
What if hyper-inflation happens?
What if hyper-inflation forces the US government to issue new US dollars with a ratio of say 1 new USD = 10 old USD?
Once triggered, hyper-inflation can take place very quickly.
And in my view, 5 years is the most we have before HI takes hold in the US.