If not the dollar, then no other fiat currency either
Let us suppose the US officially presented to the world the possibility of a 40% haircut on its debt. Would that be the same as an Argentinean haircut? No way José, since the day after the US would again find unwilling willing takers of US debt, and at quite low rates, because it would think that the day after the US imposed some debt ceiling that really became a real roof.
China, India? Good luck Warren Buffett, but we do not have all that much money to afford the luxury of trying.
In truth, if we would still use fiat money, then the Dollar II would still be better positioned than all other.