First off, while the scale of the US debt problem is pretty huge; its got nothin' on the financial & economic burden created by WWII. And that kind of capital flight out of US dollars shouldn't occur (please god dont let it occur) as the whole world will implode. Thats not an exageration; whole world, imploded. As in gone. Dead. Bye bye. So long. There will be an infinite void of nothing that all of the aliens fly past in thousands of years time and say "Hey, wasn't there a planet there before? Oh thats right, two decades of piss poor political and economic oversight destroyed it, my bad."
Second, I think you are right in one sense, in that the US is going to have to turn to sovereigns to fund itself. However (theres always a however in my line of work), China has come out today, probably for the first time ever, and given the US a slap on the wrist for poor management. Correct me if I'm wrong, but I don't think they've done that before. Considering they are the US' biggest debtor, they've got a real vested interest in, you know, the world not imploding. Given this, I don't think we'll see a big calamatous event unfold before our eyes - I could be wrong though as things are kind of unprecedented right now - its more likely to be a gradual process of unwinding positions and dilluting portfolios away from US treasuries.
Now for my next trick, head over to the other "US is fucked" thread.