The US will fall only if military bases in japan, korea etc.... begin to close down but I don't see that happening anytime soon. The US will be the sole hyperpower for quite a while.
Why would the fall of the bases = fall of American might? It may limit it a bit, but our navy gives us a wide range, and that includes carriers for our planes.
Army is another matter, but we'd still be able to at least maintain power over the Western Hemisphere with that.
The bases, as I know, are important as re-fueling depots, with or without troops. I'm sure we could find some sort of alternative if necessary. Perhaps some massive expansion of the navy to support this purpose? Mobile refueling depots, as a bonus.
Also, military power ultimately derives from economic power. The US is the foremost economic power in the world. I say this because the EU doesn't count until it becomes a fully-functional government, and so it can take its 16 trillion dollar economy and shove it.
my guess is, there will be trouble at first, but the world will normalize in a few months or a couple years.
Which is why the American collapse will be celebrated with fireworks that put the 4th of July to shame... meaning, we nuke the entire world, making it impossible to recover. After all, if we can't have the world, no one can!
Though seriously, yeah, you're probably right. Though I've heard some argue that Russia would use its nukes before allowing them to go obsolete...
I still think we need to take the nuclear option to its most extreme meaning, however.