If your fear is instead a flood of terrorism into China through those border crossings, that's an entirely different problem than having a "Ukraine" on their hands. Given the last decade's struggle to secure Xinjiang, I suspect that would be the kind of "war" China is now more than ready for. Winning the hearts and minds of the Xinjiang population was a big step in that direction. Especially the young (fighting age) generation is much more patriotic due to the education, qualify of life, and opportunity they had been given. Hence why the US and West fought so hard to deprive Xinjiang of trade/supply chain opportunities via all the fake slave labor and fake genocide propaganda.