Here is the deal: PRC takes out the Kid and the U.S. withdraws from South Korea

Cato's 'Convincing China to Coerce North Korea'

U.S. should indicate to China that its increase of military strength in the region is logical if it were meant to secure the intertwined logistics of Southeast Asia's prosperous tech economies and then point out that an out of control North Korea puts the chain at risk. Point out that for self preservation South Korea requires an American presence when the North threatens with nuclear arms and rather than counter with nuclear weapons of their own that it acquired our THAAD antimissile weaponry to defend themselves.  Point out that Japan and Taiwan may want to do the same. Point out that a misjudged nuclear conflagration would happen in their sphere of influence and may include China as well. Point out that asserting its strength and influence by invading, taking out the kid and annexing the country would be a logical means of securing the regions logistic chains of prosperity. With the irrational threat taken away American troops and the THAAD missiles could then be taken out of South Korea.