SamuraiBlue
Captain
Generally agreed with logics. But two comments though.
1.
I am sure "not need" is a certain thing because the existing treaty. Whoever is left in control is one of the existing members of the current government who can only survive with China's backing, forget about surrendering to SK or U.S. They will be throw in prison the minute they handover their weapon.
2. Because the left-in-controls are from the current government who must and surely will have Chinese backing, the "regime" will not collapse. Only Kim himself and his close allies in the leadership will be gone, cleansed, purged. The institution will stay because the majority of the ruling people will stay. It would be more akin to PRC's purge of the gang of four in 1976.
Are you guys serious?
Basically you are talking about creating a puppet state through military action.
The League of Nations didn't accept that kind of action and UN will certainly not accept either.
If PRC starts moving military force into NK without warning or request by the NK government then SK will most certainly move theirs as well to race who reaches Pyongyang first.