"It doesn't have to be paid off, Japan has national debt far in...

"It doesn't have to be paid off, Japan has national debt far in excess of the USA and has it suffered 'debt-driven collapse'?"
There is a HUGE difference between the two debtor nations.
Japan's can nationalize its debt as it is domestic.
The US debt is International because they have the privilege of having reserve currency status and may be called to pay up.
This is why it is the worst horse in the glue factory.