There's no way they invade Taiwan in a controlled manner, it's too easy to sink a navy over that distance. Sure they could do a long range bombardment but then there's nothing left to take.
This is irrelevant. Not because you're wrong, but because you're thinking of terms of what a rational, reasonable person would do. Taking Taiwan has about as much to do with helping China as the Iraq War had to do with avenging 9/11: nothing whatsoever. If China attacks Taiwan it will be for the sole reason that Xi Jinping has and is using it as a political tool to amass power. For that purpose it doesn't matter if Taiwan is a smoking crater by the end.