Nah, that won't do. Korean ultranationalism has to be uprooted in its entirety - Just like how Xinjiang and Tibet separatisms are dealt with.The only region here that's going get rejoined in the future is South Korea, after their TFR reaches 0 and gets depopulated, Kim will just roll in reclaim the now empty southern territory.
Instead of letting Kim roll over the peninsular, China should annex both Koreas and (re)unite them under the direct administration of Beijing as the 29th Province of the People's Republic of China.