Best case: Everyone defaults.
Then, when the banks fail (again) we DON'T bail them out.
Reform Federal Reserve so that money creation is done through public, member owned, and not-for-profit banks: eliminate private banking representation on the board. If we're going to subsidize banking as if it were a public good, we should operate it as a public utility.
Institute simple yet gradually progressive tax system to pay for remaining public obligations. Eliminate deductions/exemptions/incentives/payroll taxes.
There ya go. All debt-related problem are solved!
Worst Case: Get ready for 30 years of austerity and a violent awakening that gives way to the unraveling of empire and an even more violent crisis that shakes the very foundations of our government & corporate economy.
What do you want the next 70 years to look like?