Taiwan would be destroyed in an invasion, TSMC along with it. China would then have a de-facto monopoly on semiconductor manufacturing. This is why the manufacturing needs to diversify geographically.
Samsung technology is used mainly for memories. Why? No idea. In any case, people would have to migrate their workflows which would take time, and then manufacture there. This would cause huge delays / price spikes
There are other chip manufactures in the world too if people are willing to buy outdated technology (like 10 years in the past)
Also intel is investing a lot in manufacturing technology, it plans to be better than TSMC by 2025 iirc. Will it happen? No idea, but they are working toward this. I wouldn’t be surprised if the US government were financing this in some way