gold, page-100856

Sure, China or anyone else could refuse to accept US$. But their customers can only pay wit the currency they have.
China could demand payment in gold but that would just mean their sales plummet because hardly anyone has gold.
China also imports a lot of raw materails which it pays for with US$, so they would have to get their suppliers to switch as well.

Maybe the change will be gradual and many different currencies will replace the US$, but that would just slow the process even further.