solarz
Brigadier
None of these scenarios are politically realistic.
Once the NK communist regime is gone, North Korea will be history. The NK people will want reunification with SK who would basically annex NK (like what happened in Germany. The unification was basically an annexation of East Germany by West Germany, for obvious reasons).
And why would the unified Korea want to ally with china? Japan is not an enemy of SK. Most of all, SK is a treaty ally of the US, and so is japan. The US is the true power between them, and always been since the end of WWII, which was 70 years ago, a lot of time already. Don’t get illusions. SK will not ally with china. If anything, china perceived as an enemy of SK, which has maintained the division of the Korean peninsula with its support of NK, which is the arch-enemy of SK.
Once this regime start to unravel, the only way of china to salvage what is left of its interests in the Korean peninsula, is to militarily occupy NK (support of someone of the ruling regime would help) and impose conditions for the Korean unification: US pullout of Korea and end of alliance with the US. Korea would be a neutral nation, if SK would accept that.
Of course, china would be on its way of becoming an international pariah in doing so.
While I'm not saying the scenarios presented above are particularly likely, there are a few things wrong with your analysis. First, you assume that SK would gladly annex NK. That is far from the truth. Germany spent a tremendous amount of resources in order to re-integrate the East German population, and East Germany was not nearly as destitute as NK! Where would SK find the funds to create jobs for 24 million North Koreans? And if they can't find jobs for these people, what do you think will those 24 million people will do?
Secondly, SK has been distancing itself from Japan for quite a while now. First, the military intelligence pact was scrapped amid widespread public anger. Then the newly elected SK president was seen cozying up to Xi. Now SK has apparently all but acknowledged China's ADIZ and have even expanded their own ADIZ at the detriment of Japan.
The Korean situation is very tricky, and I for one do not see any easy solutions out of the current stalemate. However, I do think that it would be a mistake to consider it in isolation of other events, such as China-Japan relations, and possibly even Cross-Strait relations.
Taiwan, Japan, and South Korea are the three strongholds that USA has built around China. It's pretty clear that China has been actively wooing both Taiwan and South Korea. Because of historical issues, friendly relations with Japan is all but impossible. Without those 3 states, the US would be powerless in that region. Therefore, when considering its options on the Korean issue, China needs to keep its eyes on the real goal.
When Mao sent the PVA into the Korean theatre, the goal was to keep a buffer zone between NW China and US military. 60 years later, that is no longer such a crucial concern. China has sufficient strength to repel any ground invasion, even one spear-headed by the US. Thus, the status quo is maintained out of inertia than any real advantage.
That said, the inertia is not just a minor detail, but truly the elephant in the room. The biggest concern for both China and SK is what to do with NK refugees should the NK regime be toppled. Neither nation wants to deal with millions of refugees flowing over the border, and neither do they have any idea on what could be done. In fact, I think that is the real reason China wants NK to modernize. I suspect the Kims are aware of this, hence why I don't hold any hope of them doing anything other than just paying lip service to Beijing.