I am not going to rehash history of that era with you, it isn't relevant to the matter at hand, I think I made that fairly obvious already

"but an actual war on that peninsula would last days not years.", I'm talking about a war between Koreas, an open conflict between the US and China is another situation. We have a major edge in conventional war, and they know it, but I don't read tea leaves. As to your suggestion they'd be afraid N Korea would nuke their capital or threaten to, in order to force them in as an ally, I never underestimate the apparent craziness of that country but 'fight with us and die or die' isn't a very good card to play to court allies. If they went along China would essentially be forced to gamble the US would absorb/eliminate NK nukes and still be in a mood to negotiate a cease fire with them afterward and while they were still in some sort of position to recover. They might tell NK to go to hell or call us and warn us or attack NK themselves or they might wade in a token fashion or a genuine fashion. Like I said, I don't read tea leaves.

And throw in their generals telling them that we'll sink their fleet in days and blow every plane from the sky and cutoff every pipeline and tanker and freighter while bombing the fuck out of every base they have and that the nuclear situation isn't favorable to them either. I've no idea what they'd do, odds are they don't know what they'd do, but injured pride doesn't tend to result in ordering an attack on your vastly superior enemy who is also close friends with most of the other big boys and notoriously vengeful and militant.