The only limit I can really think of is where America becomes lower than much of the third world due to our creditors being unwilling to offer up much more in loans. At that point, currency will inflate, the government will complain but continue trading, because there simply is demand by the American populace to buy the cheap, foreign products. Frankly, the days of the West ruling are coming to a close.
Once the rest of the world flees our debt auctions entirely, it will be mandated that your private 401k or pension invest, say 25% of its value, in government bonds. It will be sold as making sure the portfolio includes a portion of “safe” (no interest) US government bonds. Justice Roberts has already established that the federalism can compel your purchase of a service.
Under your scenario Europe will reach this crisis point many years before we do. And the ChiComs and Saudis will have their “oh, shiite” moment when they realize the music has stopped and they don’t have a chair.
Some excuse to float more credit and keep the music playing will ALWAYS be found.