debt =/= bankruptcy. Unrecoverable debt is bankruptcy. While the argument could be made that our debt is past a recoverable point, it is not a certainty.
I'm not sure it could, unless I'm misunderstanding. The US could print up 15 trillion dollar notes tomorrow, and pay off all of it's debt. Of course, this would cripple the economy in a matter of hours, but it would still pay off the debt.