The Chinese don't even seem to know what incredible advantage they're holding in their hands right now.

This is what we're looking at...

[link to en.wikipedia.org (secure)]

... with China, North Korea, and U.S. playing the major trio. The rest of the players don't make any difference.

Of these three, only NK seems to be trigger happy. Once NK commenced invasion (or liberation, depending on how you look at it) and the U.S. got involved, China could provide NK with the perfect anti-air and anti-sea umbrella for this North Korean kinematic action (being on NK territory, this umbrella would also provide perfect plausible deniability for the Chinese; "We sold them those weapons years ago. Is U.S. military intelligence so incompetent they didn't even know that?").

Sooo...

Noticed any surface-to-air and surface-to-sea missile systems crossing over the Chinese-North Korean border recently? You haven't? Ah, well then... no need to worry about anything.