China wants to get rid of North Korea sometime soon, senior officials are talking about it, and they're not really giving them strong support anyhow (just enough to keep the government alive). Pretty easy to see that they consider DPRK a pain in the ass, I'm guessing they'd be willing to work out a deal with South Korea like, we get rid of the DPRK government, you take over, you get rid of American presence on the peninsula deal?
. Besides, the South's army is quite strong at any rate and as mentioned the North's ballistic missiles are all failing.