As I said above, that's only true as long as the U.S $ remains the world reserve currency/petrodollar.
If we're ever in a situation where America stops being the world reserve currency, we're going to be killing each other over cans of beans, so it won't really matter anyway.
Not really I could imagine realistic scenarios where USA stopped being the world’s reserve currency, and in most of them USA would still be functional and a first world country. But you’re right the existing deficit would be completely irrelevant.
A important point is that if the dollars stopped being the world reserve currency, the American existing debt would still be in dollars, and as such it would fall together with value of the dollars.
