The realistic scenario is that the Taiwanese elite does a deal with the CCP.

America is nobody's friend, at the end of the day China are still Chinese. Americans are xenophobic and racist. Increasingly anti free trade and isolationist.

Also I am incredibly sceptical that the US wants to go to all out war with China over Taiwan. A war they aren't even sure they can win and that REGARDLESS OF OUTCOME will leave Taiwan in ruins.