If china were to deal with the Korea peninsula, the problem to deal with its own security.
Nk is working to advance thaads and US troops closer and closer to the Chinese borders in exchange for technologies.
Sk is playing along getting free military protection and equipment.
China / Russia must made clear to the world that the Koreas are working together to jeopardize their sovereignty and security. Corrective action is not far away.
South Korea is actually living an unrealistic dream that is unsecured and parlous.
They are the center piece of the US's "NK theater". Both nk and sk are sacrificial lamps.
The bigger the damage to sk, the bigger the US presence. This is the goal for US and Japan, not for China / Russia and absolutely devastating to Sk as well as nk.
--Update--
Just 15 hrs after I posted this, this story broke