The TSMC fab in Taiwan is the world's most advanced. There are no other sources for 7nm manufacturing at the moment. Moreover chip designs can't just be immediately re-spun onto older processes: if it were lost to China then basically the rest of the world would completely lose access to a fresh supply of the best chips. Tech would immediately have to roll back a generation of two, hardware wise, and of course software that relied on that performance would also need to roll back, etc.