I'm sad that you don't realize Taiwan is already functionally autonomous, and wants to remain that way.
It's also telling how you imagine that a typical American wouldn't "let" Texas leave the union.
As far as I (or anyone else I know) cares, if Puerto Rico or Guam or Texas wanted to leave the U.S. (which they don't), and they held a vote, and a supermajority voted to leave, why wouldn't we let them leave? It isn't the 1860s anymore. The world is much more democratic now, imperialism is over, and if a group of people want to go it alone, we should let them.
Scotland had a vote to leave the U.K., and they decided to stay, so they stayed. If they had voted to leave, they would have left.
The U.K. had a vote to leave the E.U., and they decided to leave, so they did.
Would China recognize Taiwan's independence if Taiwan held a vote? Of course not. The reason for this is not merely because China doesn't sympathize with the desires of the Taiwanese people, but because China doesn't even believe in democracy in the first place.