North Korean conventional forces have really deteriorated and get weaker every day; what little resources they have they're pouring into strategic weapons.
They'd have no chance of making any progress with any sort of land invasion of South Korea, and they know it. Or they would have tried it already.
The Chinese have no particular interest in any such a war happening; the overwhelming concern, from their perspective, is preventing millions of North Korean refugees from crossing their borders. They'd prefer to keep the DPRK around, of course, rather than having a unified Korea under Seoul's control, but they'd rather have that than the refugee problem.
Interestingly the ROK government really doesn't want a unified Korea and doesn't want to have to pay to rebuild the North, either.
I wonder though, might the Chinese be goaded into something should the Il one decide to go on his own?