China's policy is one of minimum retaliation.
I should clarify, I read your warning as the thought "the next strongman" will continue being a dictator who maintains an independent and oppressive nation. I don't see a reason or need to push over NK's leadership, which I think is what you are concerned about. However I see the possibility it will be pushed over internally from coups or liberalization. In that instance, I don't see an internal strongman taking over save one who facilitates the transition. But even in the event of the very unreasonable invasion of North Korea, I don't see a strongman who perpetuates the existing policies. Hitler was replaced by an admiral of the Kreigsmarine, itself the least political arm of the military. This doesn't seem analogous to Iraq or Afghanistan nearly to the degree it is analogous to East Germany. If the existing regime weakens or ceases to exist the country I can only imagine it folding into South Korea and, after a not-insignificant period of disruption, become at least a place where people have food and aren't thrown in concentration camps.
Unless China moves in to secure the destabilized country with the army they've already moved to the border, and annexes it.
Goddamnit.
That is a real stare-down to war, but I hope Xi has less interest in economic exclusion zone waters falling to a US aligned Korea than he wants to rebuild the North Korean economy and feed its millions.
Things just get better, folks.