Alright this has gone off topic.
Point is if China decides to make a play at Taiwan, unlikely that anyone could stop them, but they would suffer heavy casualties shortly after taking the Island. The Western allies surge their Navy/Air Forces to the Western Pacific - 6+ American Aircraft Carrier groups, 1-2 European Aircraft Carrier groups, dozens of Submarines and landing craft. That’s over 500 advanced carrier based aircraft alone. Not to mention air based in Okinawa and the Philippines. There is no way China will maintain local sea superiority and Taiwan can be retaken.
If this situation were to occur, China would be embargoed and the world economy would suffer. Other countries around the world would take up the slack, more than happy to produce cheap goods for western investment- Vietnam, Mexico, Brazil, India, etc. This is a no-win for China.
North Korea is another story- if they made a play for the South at the same time (presumably the world would be distracted by China), there are three scenarios I can see:
1. China aides them. Unlikely, but would be extremely difficult to prevent a complete overrun of the South. Do South Korea/US have enough bullets? It could also depend on whether South Korea/Japan/US could get air superiority. China has gotten better fighters recently, some of which technically can go toe-to-toe with our modern fighters. Can South Korea/Japan/US win in the air while outnumbered?
2. China doesn’t aide them. North Korea runs out of supplies in a month and South Korea/Japan/US push back to the original line and another ceasefire results. Status quo here.
3. China doesn’t aide them. South Korea/Japan/US decide to push all the way to China to unite Korea and remove the dictatorship in the north. Kim Jong-un uses nuclear weapons in a desperate attempt to win and thousands of South Koreans/Japanese/Americans die depending on his target. The US retaliate and North Korea is a nuclear wasteland.
Anyway, its how I see it.