Best case scenario:
>China intervenes in North Korea
>Offers to take Kim, his family, and the top generals into China in hiding for the rest of their lives
>Give it to Kim like this:
"You and your buddies can come with us, live out the rest of your life in a nice mansion in BFE china and never have to worry about anything and we spin a story to the people about some new general or high up politician taking over. Or we can kill you and your family and loyal generals overnight to install the guy anyway"
>China slowly turns NK into a Chinese territory that's connected enough to sustain themselves and transparent enough to prevent a war on their border.
Kim currently only has one objective at the moment: staying alive. He knows he can't transition to a democracy and globalize the country, so he keeps up his regime. How long does he have until his people question the famines, work camps, etc. over the decades? And that's just within his own country. What happens when the ICC and various other countries bring him and his regime up on charges for crimes his operatives or military carried out over the years?
Take South Korea as an example. Following the Korean War, the US invested a ton in the country technologically, built up a huge military presence in it, and turned it more or less into a psuedo-US state. Since the war, the US has supported some unsavory leaders, allowed the May 16th coup, and supported Park, then his assassination, etc. Look at the huge developments in the country. Up until the 70s, large populations in the country didn't even have electricity, now look at it.
This is probably what's going to happen in North Korea, but with China investing heavily in the country and stabalizing it behind the scenes. Yes, the North would still remain poor for a long time, no they wouldn't have a real democracy for a while, but there's no refugee crisis; no destabalizing war. Eventually, the DMZ demilitarizes and China gains a new economic ally.