Wouldn't make sense for them to go to war with each other.  China has far worse debt problems than the US.  They'd be better off joining forces and attacking someone else.  Reaping the huge profits to pay down their debts.  I'm of course not advocating such BS.  Just saying.

That said, Bitcoin prices would likely plummet, as such a war between these two debt ridden nations would destroy both economies, level infrastructure and leave basic necessities like food, water and shelter significantly more valuable than some "boutique" internet currency.  Let us instead hope for a peaceful transition between government fiat and digital currencies.