Yes we would need to immediately start running a balanced budget. It would probably be a long time before we could borrow again. If we ever did borrow money again, we would be paying a higher interest since we've shown lenders that we can default.

It would also mean $33T in assets disappearing from the economy. That's a massive amount that would bankrupt tons of individuals/companies that lent the money. $2.8T of that amount is the social security trust fund which means we need to also instantly cut social security too. $7T of the debt is held by other countries who wouldn't be happy with us either.