This is the Chinese’ mess, and it would be safest for them to clean it up. A three step solution. Invade, capture their nuclear weapons, decapitate their government and replace it with a more pacifistic puppet government committed to economic and agricultural improvement, and leave.
The benefits to China would be tangible. Restoration of peace on their border, a lack of refugees or even a negative illegal alien Korean flow back from China to North Korea, a “safe” government that will not reunify with South Korea, and cooperate with the Chinese in all things, and a deescalation of the regional nuclear threat. Plus, soon North Korea would stop being an economic basket case consuming lots of Chinese aid, and start trading with China for what it wants.
It would allow the US to ignore the region a lot more as well, yet another benefit to the Chinese.
But President Trump needs to be very clear to China that either they clean up their mess, or the US will have to, and China will not enjoy that at all.
And US has to punish China for not cleaning it up. China should get painful economic retaliation which can derail all of Xi's purported grand vision. That should be made clear to Xi.