Let South Korea & Japan go nuclear and develop missile defense technology. Tell China you have had X number of months to fix “the problem”. You didn’t this is the result.
Oh yeah and that MFN on trade status you like, that’s gone too.
Just tell China they can have North Korea if they want it. If they don't we'll take it for our use, or to make it a part of Japan or South Korea, or sell it to whoever puts down the largest bid.
NK would be gone in a year.