Marc Faber and others are sure they'll deal with it through money printing. i.e., if the USD devalues by 50%+ over say 3-4 years their current debts will halve. It will also likely significantly help the derivative time bomb as most of that stuff is priced in nominal USD.
This is why US long dated tresuries could be in a huge bubble, but Ben bids them up on the market with printed money. They do this because they can't afford rates to go up anymore.
It's been one of the only economies in history to have it's foreign debt in it's own currency. Other basket cases in the past used USD not their own currency and this is why they defaulted, as their own currencies collapsed.
So I think you're probably right, they're very unlikely to default.
