The author does know that the US has never promised to pay back debts in US dollars in anything other than US dollars, right? There never was any promise to pay back with "real" money (as if such a thing exists!)

At any rate the US is in no danger of going bankrupt. They do run a certain risk of having their purchasing power decreasing, but of course their exports will automatically become cheaper for other countries to buy, which will turn around the balance of trade.

The real risk is being run by those that are holding large balances of US dollars - they risk taking a bath if (or when) the US dollar is dramatically devalued. But then, they knew that going in, so I have limited sympathy.