The foundries are the main (only?) reason for China to take over Taiwan at all.
Not quite. Think of Taiwan as a big, unsinkable Aircraft Carrier permanently stationed in the Pacific.
Plus, lots of educated, industrious people who are Chinese. They built those foundries, so presumably they could be rebuilt.
And, lastly, the boost in China’s reputation as a world power.
All that being said, I doubt the US will be caught as flatfooted as the article suggests. It is also possible we may attack first if we think a Chinese invasion of Taiwan is imminent. Preparations for an operations that size is a hard thing to hide from Intel.