If China is serious Taiwan will be encircled with s-400's in little islands(artificial or otherwise) surrounding it before the first shot is ever fired, at which point the conclusion is already a forgone tale.
When it does happen the rest of the world(by which i mean the U.S) will be pre-occupied with domestic issues, cyber space issues and possibly another pandemic.
Not to mention the backdrop of the fact that the U.S launching missiles to China might trigger the MAD doctrine of Russia because missiles heading in that general direction might as well be heading to Russia, or be assumed to be as much.
>“Russia will perceive any ballistic missile launched at its territory as a nuclear attack that warrants a nuclear retaliation” - Russian military chief warned last year after round of reforms
Ergo the U.S president at that time will leave Taiwan out to dry instead of risking World War 3.
We're living in interesting times.