North Korean Leader Warns Of Nuclear Disaster, Threatens US

[Benton D Struckcheon]

26. He's alive because he's a useful pawn for the Chinese

Their push against their neighbors, and in this case specifically SK and Japan, is helped by having a wild lunatic like him as an ally. You don't really want to mess with China when they've got a rabid skunk like this who may not be able to do lethal damage, but can distract you enough that when the really lethal attack begins you'll be looking the wrong way, or entirely blinded.
It's not like the US doesn't know this of course. I have a feeling if things really got hot the Chinese will find that Jung's usefulness is rather seriously overrated. Nukes are like any other weapon; they have to be aimed and fired properly. NK has given the world no evidence it knows how to do either.
So, assuming the evidence is correct and those weapons are useless to them, and then given the fact there's maybe 10 people in NK who are actually well fed, the Chinese might find themselves with a very well fed and well equipped army on the Yalu somewhat more quickly than their war-games told them they'd have to face such a thing.