They go down too. Their economies are linked to ours.
Right, debt isn’t really debt? When we can longer fund it there will be collapse the likes of which you’ve never seen. Don’t listen to the Harvard boys fables.
There are only so many ways out, once the collapse has begun: the U.S. Government can use its sovereign power of taxation to directly seize assets (not just income) of households to service debt; businesses could be nationalized and profits used to service debt; or the U.S. Government could simply replace the U.S. dollar with a new currency.
Are we familiar with the phrase "not worth a Continental"? (Hopefully yes.)
Remember that every dollar you hold, whether paper currency in your hand or on deposit at the bank, is a liability of the Federal Reserve System, backed by U.S. Government debt (mostly). If U.S. debt becomes worthless, your U.S. dollar becomes worthless.