Despite being the second largest economy of the world, only 4.3% of international trade happens in in the Yuan [1]. People do not want give their oil and wheat in exchange for Yuans! Countries do not see the Yuan as a valuable reserve currency, which reflects their trust in the Chinese system. Since the majority if international trade happens in US Dollars, China needs to trade with the US to get Dollars.
The US on the other hand produces much more food and energy it needs.
For now. The yuan is still a new currency in the world trade. The Chinese are just starting to push it as a global currency. This will take some time, but I imagine that 20 years from now the yuan will be a second, if not the first international currency.
What's your point? The only reason to point what would happen if China did close would be to show that they have leverage over the rest of the world. But if they can't or won't close, and everyone knows it, then they don't have leverage.
