If the U.S. sinks as you fear, what takes its place? Singapore???
Oh boy, I don't know. Which country becomes the economic superpower or which country becomes the military superpower? I really don't know. I don't know enough about the world to figure that one out.
I think the USA will probably fall back into pack of today's European social democracies. We will probably become indistinguishable from Sweden or Belgium. Perhaps some other country will begin to pull ahead of the pack but I don't know enough to know which one it will be.
Or perhaps it will be a Muslim country to take the lead because of the sheer demographics of it. If birth rates in the Western World stay on their current path maybe Muslims will eventually be able to conquer the world by simply outnumbering everyone else.
However it plays out, I'm not optimistic for the USA.