Continuing to be extremely interesting. What are the possible alliances?
Assume first strike by NK into SK. (where else could they strike with any hope of success, minimal and short lived as it may be?)
Would China ally with NK or wait to annex it?
(Would other nations worry that a China annexation of NK could lead to strain on SK?)
China doesn’t seem to have any power (or will) to squash Lil Kims’ tantrums (at least outwardly).
Japan would most likely ally with SK.
(thus becoming an ally of China but then a contradiction of a free Taiwan?)(shades of WWII with our “allies”).
Interesting scenarios. This may a situation where most will ignore the situation due to its totality of failure.
Doubt anything will come of it. (?)
They have agents operating in Japan in significant numbers, too. In the past, North Korea gave veiled references and threats to unleashing a WMD attack on specific US military bases in Japan, if not in downtown Tokyo towards Japanese civilians. This could in fact take the form of a suitcase nuke, which for all intents and purposes could a) already be in Japan, and b) would have the necessary delivery system/infrastructure (agents of Chongryon or other infiltrated agents), to do the deed. In fact I have noticed a considerably high presence of Japanese police and security personnel at various Japanese train stations and bullet train stops these days. Who knows what for.
China will try to defacto puppet regime in Pyongyang, and pressure other countries to accept the deal. This would make S. Koreans really unhappy. However, erstwhile pinkos, who railed against U.S. Imperialism on Korean Peninsula and so big on nationalism and Korea's victimhood under American 'boot,' would embrace it as a 'reasonable and practical solution.' They would never have been reasonable to Americans but things would be different with China. Selling out nationalism and victimhood for pro-Chicom stance. Anti-Americanism at all costs, which could erode their support among general population.
China, after installing a puppet regime, would go about buying off N. Korean population with more food and better economy. They will try to gain access to key strategic locations(ports along E. Sea (Sea of Japan).)
Security hawk will prevail in Japan now that China advances into Korean Peninsula. They will seriously rearm and could go nuclear, which would worry China. Concern for S. Korea and Japan going nuclear would be a great mitigating factor for China's design for N. Korea.
If N. Korea would fall under China, even through a puppet regime, S. Korea and Japan would less rely on U.S. Japan could try to take S. Korea under its wing, which would be resisted by S. Koreans. This will give more motivation for S. Korea to go nuclear than Japan.
Russia would try to join the fray, dangling its natural gas and oil supply from Siberia and Sakhalin as a carrot. They have wanted a trans-Siberian shipping route from Japan, S. Korea to Europe. They want to increase their influence on Korean Peninsula this way.
All this hinges on the assumption that N. Korea can be taken over with no serious troubles. However, succession struggles degenerate into open confrontation, military confrontations between factions, or even further different faction chose different outside backer. That is, one faction gets China's support, another get S. Korea and U.S.. Then things get messy. Even if somebody takes over government, but government cannot function and chaos continues on the ground(no effective government control,) drastically different situation could emerge. It will get messy for all parties involved.
China does not want NK. It's a liability. Why would China want another 25 million underfed and unhappy folk? They're trying their best to keep growing and lower those figures for their own countrymen. China's only interest in NK would be SK... or if, in the aftermath of some joint military venture into Korea, the victors have a lot of assets and aid to help make NK viable and worth annexing.