Isn't the answer to that one easy, the one with the biggest guns wins by default?  What possible recourse does the rest of the world have when the US defaults, other than to simultaneously default too?  If I owe the bank $10000 and I can't pay them back, I have a problem, if I owe the bank $17 trillion and I can't pay them back, the bank has a problem.   Whenever later becomes now, the game is officially over, as you have shown before, it is mathematically impossible, and the whole system collapses, the creditors only hope is to prolong the inevitable as long as possible.  Which has been working for decades already.

I will bet they won't be as willing to accept IOU's next time around though, which means we will have to adjust our lifestyles accordingly.