I'm curious why you think China will decline or be eliminated, I always thought that China was a reliable as a production/trading partner and that they planned for decades ahead with programs like Belt and Road Initiative unlike western politics that only looks as far as the next election. Very open to correction on this though, thinking about it not sure what formed my opinion on this.
It’s foolish to be completely dependent on anyone else, no matter how stable the CURRENT situation is. We’ve seen this with the gulf countries and Strait of Hormuz, China with rare earth metals, Ukraine with grains, etc. Once China goes to take Taiwan all bets are off…
Their aging population will pose an extremely serious problem in the coming decades.
The Belt and Road initiative is a nice try, but it's not a roaring success. The flaws of democracies are easy to see because of the openness, and whatever goes wrong usually do so over a long time. Dictatorships go wrong in more dramatic ways.
China is not a good trading partner at all. They put up barriers for companies entering their market, mandatory China employee in your company, IP theft, they subsidize and flood the market killing competition, most everything they make is lowest quality possible, lots of fraud even within China.