Aside from the Korean War, what's the recent history of Chinese aid to NK? I know they turned off the oil pipeline for a few days. To me, that's a huge break in attitude since they were sending infantry divisions marching towards the Yalu.
If I had to guess, China is too interested in their international trade standing to risk pariah status from supporting a weirdo leader of a fairly insignificant swath of east asian land.
I'm sure more familiar FRreepers will educate me :-)
China has the US by the nads as far as trade goes. IMO, they fear no one economically.
I think the Chicoms would react negatively if we attacked NK. I don't know what they would do, but because of the proximity involved, they'd have to respond for their own sense of soverignty.
Just as if China attacked Cuba, we would not stand for that.