It is. But re-integration remains a goal for Beijing. If not realistically, then at least politically.
The more aggressive Xi has been with Hong Kong, the more Taiwan has stiffened. Rolling tanks into Hong Kong would give Taiwan legitimate cover for being supplied weapons. For a variety of reasons, China doesn’t want that. That, in turn, gives the protesters leverage.
https://www.nytimes.com/2019/06/06/us/politics/trump-taiwan-...
Huh? No, it doesn't. It has military bases in nearby Okinawa, however. I'm sure the USA setting up a military base in Taiwan would really piss China off, and it would also be not very useful since the Ryukyu Islands are right next door anyways.
The USA simply provides Taiwan with weapons, and occasionally meanders an aircraft carrier around (or used to, it doesn't do that much anymore).
Taiwan existed because of the US. Basically, the other side of the civil war got defeated and come hiding in Taiwan behind US military. Otherwise, it'd have been invaded by China since.
It seems currently that there is no official military presence. However, there is this: https://en.wikipedia.org/wiki/Six_Assurances
I think it's enough to deter China from attacking Taiwan.
In an alternate dimension where Mao held back, we would have had a unified Korea and China, strange.
From my limited knowledge, the US has a military base in Taiwan. It'd be hard to invade the country without conflict with such a base. And even a small incident can spiral into a war with China. So no, I think Taiwan situation is way different than Hong Kong.