Ships may list for a long time before they suddenly and dramatically sink.
backing off the USD is a hundred year project...you need an currency from a relatively open and law-bound Great Power that has demonstrated its staying power through conflict
there isn't anyone else who fits the bill...yet
The federal government choose not to have that power, they could technically take it back at any time with only political/market confidence consequences. With a crazy guy running things, anything is possible at this point.
That's one way of downplaying what happens next...