If push comes to shove, China will absolutely not let Kim Il Jong go too far out of line. Two reasons: 1. Whether they like it or not, the US is China's single biggest trading partner, and they realize that their country cannot (CANNOT!) afford to lose that. 2. China wants to be THE regional big kid in Asia, and if they allowed North Korea to step out of line and destabilize the region... Well, it would kind of make them look incompetant, don't you think?
Although, I wouldn't put it past the Chinese government (or even just elements of it's intelligence services or military) to cook something nasty like this up, just so they could play the peacemaker. It's not like other nations haven't done that in the past, either.
I had the opportunity to speak with a high-ranking State Department official a few years ago on this subject, and I like his perspective (off the record, of course): "Personally, I think we owe those bastards a beating, and I say it's time we stop taking their sh!t."
Taking their sh!t, of course, is precisely what the South Koreans have been doing for quite a few years now. Officially, it's known as the "Sunshine Policy", and it basically amounts to South Koreans blowing quite a bit of that sun, right up their neighbor's @ss. North Koreans raid the border/Sea of Japan for women to use as prostitutes, and the South sends them aid. Kim Il Jong wipes w/ the South Korean flag...the South sends them aid. The North shoots a missile into the Sea of Japan, preps all its artillery along the DMZ, and sends an advance force through the tunnels underneath the same? ...You guessed it. How else would one of the poorest nations in the world, where they literally eat their own dead because food is so scarce, get the nuclear know-how? True, they probably got most of it from China. But the South is one of the richest nations in the world, there were a lot of families split up by the Korean War, and the DMZ is mighty porous.
I was stationed in Iwakuni for that last scenario I mentioned (it was a pre-cursor to the august 1998 launch), and let me tell you, being an hour's flight from North Korea while missiles are being lobbed in your general direction is pretty nerve-wracking.
....the deployable missiles have yet to get a good hit out of the only 2 attempted tests (the ones prior were R&D systems), or even get off the pad during a test 
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