It's so tricky, I'm just gonna say "Taiwan didn't split from China, it was China that split off". ROC gets tarred as rebel separatists by PRC, but in reality the more 'unbroken' historic government of China (well, from 1911 or so, when the Imperial system was overthrown) is the one now on Taiwan/whatever, and it's the rebellious communists of the mainland who (in 1949, four years after Potsdam, six years after Cairo, where then-Formosa was declared to be rightfully Chinese by the Allies) snatched much of the ROC's territories and left them with Taiwain.
So, really, any talk of 1,800 years of history and rightfulness is effectively scuppered by a whole lotta "things are different now". Really, there are many similarities (by different scales) to the "Ukraine belongs to Russia, it has always belonged to Russia" claims.
Not that there's absolutes to this, but any post-WW2 "Right, everybody stops invading anyone else right now, none of this new Empire Building shit" does not support One China.
Force and/or Popular Movements might, as it has supported other changes in the world map over the last 3/4 century or so... That's a different thing. Just don't appeal to the precedent you choose, because it's not the mike-drop you(=generic) might think/pretend it is.