[sudosysgen]

It's not a diversionary state, it's really just a buffer, ie, not immediately hostile.

It's very very well documented that the Chinese are incredibly displeased with Kim Jong Un. Plenty of retired generals talk and write about it.

NK's population and military breaking away without outside support is far from guaranteed to bring a better outcome for anyone. It's not clear to me a military dictatorship is going to be less brutal or repressive than the Kims and it's not clear either that the population could ever break from the yoke of the military should the Kims lose power.