I guess we'll find out before too long, but you're overestimating the Chinese military's strength, and the US's determination to win at all costs. An attack on the US mainland would absolutely be met with a full-scale nuclear attack; the US has never been attacked on its own soil before in the modern age, except for 9/11, and the results there were catastrophic. A serious attack would be all-out war to the end, regardless of any long-term consequences for humanity.