Why do you assume China will take over as a superpower? It’s certainly not the case historically that there’s a single global hegemon.
Also, I use “empire” because people are justifying our having military bases all over the world on that somehow benefitting america economically. I am not sure I understand why—forcing the world to use dollars as the reserve currency seems to be part of the theory. But if that’s the case then empire is an appropriate label.
And stop being disingenuous by labelling the current US-led global security system as an "empire". Words mean things and I'm sure you're smart enough to know what a real empire looks like, so I can't imagine what you think you're accomplishing by trying to frame the debate that way.