Even if this happened (which I very much doubt it will because Japan, China etc. don't want to write off 40% of their holdings or get into a vicious economic war with the US), that's a long way from hyperinflation and general fiscal Armageddon.

US business would love the dollar to fall by 30%, our exports would soar and those companies that depend heavily on manufacturing in China could probably use other hard currency like the Euro. It would crimp our military operations overseas, but when you get down to it a lot of countries still want to be under the American nuclear umbrella and we paid for the nukes a long time ago.