China is very important but the shipping lanes to SE asia and regional stability is more valuable. You can sanction China and get in a sanction war with them until one side gives in. Or a trade war like trump tried.
Their focus however is to win the war before it starts unlike the US which is to win the war after it starts (imo).
If it gets to a full in sanction like russia, the western economy will tak a massive hit, but it isn' beyond recovery and might actually be good to force resilent supply chains. Especially with silicon fab.
I can't tell you what will happen if Taiwan is invaded tomorrow, next year, or twenty years from now, but I can tell you that the US will think long and hard about whether or not it will want to get involved. And it might well choose not to.
How many years do you think it would take to build up those resilient supply chains? 5 years?
That's 5 years without most products from AMD, Nvidia, Tesla and every other TSMC customer. Samsung can absorb some of that business, but not much. Intel will shoot to the moon in that scenario.
The US _did_ have a mutual defense treaty with Taiwan, but it was terminated by the Taiwan Relations Act after the US initiated diplomatic relations with the People's Republic of China on Jan 1st, 1979.