I agree that the most likely scenario is status quo. I doubt that Taiwan will volunteer to join China.this possibility has always been overblown by Westerners. most probable outcome is it won't happen and both sides continue the status quo indefinitely.
if you like your doomsday scenario though, China would almost certainly take out Taiwan's power grid during an invasion and global chip supply chain would be severely disrupted.
after the war it's anybody's guess. China could lock down TSMC and hoard all the leading edge tech for itself. Western countries would try to retaliate through sanctions but that will hurt themselves equally due to global reliance on Chinese trade and manufacturing.
If there is an actual hostile take-over, Taiwan and TSMC could be cut off very rapidly from any and all technology made in western states, such as all scanners. And most non-litho tools. That would relegate TSMC output to obsolescence rather quickly. Plus, embargoes could then also be implemented to other Chinese companies like SMIC. It would not work in China's favor.