That doesn’t make any sense. The US has access (and is the source) of global capital because of our markets, laws, and strength of our economy. China won’t supplant the US because it’s a communist dictatorship that disappears people which means folks including the Chinese don’t want to keep their capital in China.
Second the OP said “no longer #1” which can take many forms including still being the dominant reserve currency. Also UK isn’t doing too bad see: UK not doing too bad.
losing that #1 status also means you have to work for a living, rather than just printing dollars and debt. see: britain
everyone in the west except the US already has to deal with that, so we'll be fine