The odds of them winding up in a Russia-Ukraine are not nil. (Combined-arms war is hard even without ideological purges.)
America isn’t only outside power investing not only in helping Taiwan fight, but also making any victory pyrrhic. And following that, we’ll see Indian and Japanese containment go into overdrive. (To say nothing of the Philippines or Vietnam.)
I think Xi probably takes Taiwan. But that trades off China’s century of prosperity on economic and diplomatic fronts. That’s the trap the West has been laying, and Xi’s ego and internal constraints almost force him into it.
(Again, if China had showed its pre-Xi patience in the 2010s, we might have seen Taiwan voting to unify right now. Instead he rushed things for personal glory and enrichment.)
I agree with you about Xi's impatience but I think you're overestimating the political and economic fallout in the same way that people overestimated the ramifications of China retaking and consolidating its control of Hong Kong. The latter is definitely not politically free in the way it used to be but nor has it fallen into decline or dystopia.