Agreed. China is in the driver's seat here. If China decided to pull their support from North Korea, the whole place would collapse. Of course, that would send millions of refugees into China, which is exactly what they don't want. South Korea would be thrilled if they could just merge / take over North Korea in the same fashion as Germany reunified. If China pushed hard enough, maybe something like that could genuinely happen.

Amusing thought: if China truly wanted North Korea and South Korea to merge, what would they do to make it happen? Can they do it without military action?