Debt is not a sword of Damocles hanging over the US. Debt is basically China having sent a bunch of actual stuff to the US in return for a promise that the US will make them whole sometime in the future.

And because of inflation, the value that the U.S. has to make China whole by keeps reducing.

If the US sand China went to war, China could keep waving those pieces of paper and the U.S. would simply ignore it.