I am a currency trader for a while. The reason USD survives because there is no other game in town. The reason there is huge demand for USD is because even the largest economic enemies of the United States, hold massive amount of USD and USD backed assets. There is a case against USD touted for last 20 years. The fundamental argument in favor of the bear case for USD is solid. Even Buffet shorted USD in the late 2000s and early 2010s, against the EUR. One of the worst trade BRK-A did in their entire history. Now, Buffet has very deep pocket, so he managed his loosing trade much better than a regular individual or a govt., but still he incur massive losses that would have broken almost any other entity.
My point is, as long as Chinese Govt, and Chinese Private equity funds, and rest of the world's private equity funds continue to hold US Govt. Bonds and USD backed assets. There is nothing that is going to happen to USD.
Ask yourself the question: What else would you rather buy? Euro? LOL. That is similar to buying Iraqi Dinar! :)