They just conquered 10% of Ukraine, so they might do that 10 more times.
> Why would China get involved?
Biden has been quite explicit that he wants Putin gone. If NATO triggers a collapse of the Russian government that would be very bad for China. They want a stable Russia. At some point they'll get involved in this if it looks like NATO is going to keep escalating the situation.
> How? They tried already.
They walked in, were surprised by unexpected resistance, walked out and resorted to taking back the parts of Ukraine that prefer to speak Russian. There isn't much in the way of reliable information to decide if it was that they can't destroy Ukraine or they don't think it is useful to do so.
These are all hypothetical scenarios because it is a war and figuring out what is happening in a war is tricky because all the players start lying. But it is hard to see how keeping this war going will improve the situation. There are a lot of ways this could go even worse. Which is something Kissinger has been pointing out recently - even he can tell at 100 years old because it is that obvious.