US will still have plenty of reason to defend Taiwan, if only because it is a crucial part of America's containment strategy - China would have a much easier time operating in the Pacific if it controls Taiwan, and the US won't allow that. Further, if Taiwan falls a lot of countries will lose faith in America's ability to protect them from China which would thrust the entirety of South-East Asia into China's hands, also something the US can't afford. Though, with recent claims that China can build 1000 cruise missiles a day[0] it might not matter whether US defends them or not.
[0] https://asiatimes.com/2024/03/america-has-no-ukraine-plan-b-...