The Taiwan Relations Act is not really binding on the U.S. since we shifted recognition. Not that there won't be strong Congressional pressure on the president to act on behalf of Taiwan. But there is no official military alliance between the U.S. and the ROC.
I'm not sure why you think it's not binding since recognition shifted– the Taiwan Relations Act was passed after the US switched recognition (so you're saying it's never been binding?). I would presume that any provisions that are phrased as being binding are indeed binding unless the Act is repealed.
Maybe you could clarify what you meant by "binding"? Of course the Act can always be repealed so if you meant that there are no international law obligations, then you're likely correct there. But I think that as long as the Act is in force, I don't see why it isn't binding.
I didn't mean to imply that there was an official military alliance, but the Taiwan Relations Act authorizes the US to treat Taiwan as if it were a foreign country (I assume you can't sell weapons arms to private parties or rogue states). It also requires the US to make defence articles and services available.
Also, the Act leaves some open-ended possibilities that the US won't comment on- most notably military action. If that's a looming possibility, however unlikely, it will make China think twice before invading Taiwan.
IMO if China's going to take over Taiwan, it'll be mostly economically and culturally, not by military might.
