I don't believe anything will happen. Everyone has too much to lose, and absolutely nothing to gain. North Korea Collapsing is Bad for China, Bad for NK, and Bad for the USA who financially backs SK, no-one (intelligent) really wants it to happen. However, Militarily It would allow the USA to position troops in unfavorable positions for China. Amazingly, the USA has already begun attempting to surround China Militarily. SK/Aus/JP are the major US positions atm. This was a huge deal a few years ago in the media. Still is, just don't hear about it as much. We have nearly 400 Military Bases around China presently, While China doesn't have a single one near us.
https://www.antiwar.com/blog/2014/02/25 ... onversely/
North and south Korea uniting is bad for China, they don't want it to happen. (The south is far more powerful, rich, and influential.) If they reunified, the south would almost certainly lead the charge. Thus the USA would gain a foothold that China would never tolerate.
The US can't afford to REALLY piss off China, they are a very powerful country, so we will not simply invade or preemptively strike NK as ppl have said. Won't happen. The US, and China would never go to ear either; they may have "Unofficial" Skirmishes, but it would never go beyond that.. Same as with Russia. Any of those 3 countries really fighting would be the end of the world, not to mention if the US fought either; it's pretty much a certainty that the other would join up against the US. Since the US is a shared enemy; at least more so than they are to each other. This would almost certainly result in nukes being used. So the US won't Strike, or Invade Period. (Then again, Trump is insane, arrogant, and stupid as a rock; well that's an insult to rocks, sorry rocks.)
North Korea will NEVER strike first, because if they do they will be annihilated, pure and simple. They would be able to cause a MASSIVE amount of destruction, damage, and death before going out... but they would lose, and lose fairly quickly, and they would lose everything. So won't happen.
The best thing that could happen is for everyone to try to calm NK the hell down, stop sanctions on them. Treat them better, provide more real assistance, and let them join the UN nuclear council, in exchange NK becomes a modern country on a major NATO council, and would be able to build up their country, fix their issues, and become self-reliant. Being part of NATO they would also have to change their standards of living for the citizens, they would have to open up to arms inspections (Just like every other country with nukes.)
It wouldn't happen fast, or without issue, and definitely not without some sacrifices, especially moral ones. But eventually the breed of North Korean that see's everyone else as Villians, and Monsters out to get them will die out, and new generations will be born... raised in an era where they are getting help, tourism, information, and other products/imports from these countries.. and will no longer see the devils that they have been brainwashed to see now. Kim Jung Un will eventually die, so will his supporters, and inner circle; eventually his influence will wane, fizzle, and disappear along with him.
In fact, the richer, and more stable the country becomes.. the better for everyone. The richer the population gets, and as laws/etc become less strict, and they are able to get real info/ maybe use a restricted form of internet, (ppl will always find a way past censorship, just as in China.). Citizens will begin to resist and attempt change from within. Even the rich would probably rather live in a modern, rich, and safe country. Free from fear of being imprisoned for any random reason, and send to death camps to die. Free from fear of invasion, and living under the foot of an insane regime.)
A stable NK Keeps the US from positioning troops in places China doesn't want them, and SK and the USA don't have to worry about either direct NK hostility, or them giving away nukes to terrorists, or their country falling to pieces, and nukes being stolen by terrorists, and other radical organizations. The South doesn't have to worry about a MASSIVE influx of North Koreans seeking shelter/aid, and needing to relocate. In fact, it could eventually lead to them having a better political association, less aggression, and being able to actually trade, and benefit each other economically.
But yeah, Humans are stupid, violent, and greedy barbarians.. It likely won't happen, at least anything that clean, direct, or positive.
Sorry for the long ass post, I'm just tired of hearing about all the Aggression, Potential Wars / Nukes / WW3, etc.
There are so many alternative solutions, and yet none of them are pursued. It's just plain sad.