It's reasonable China and ROK would come to an agreement where China helps stabilize northern Korea in return for US troops off the peninsula. Once ROK is ready to assume responsibility, the Chinese Army will go home.
I think the chance of an amicable resolution to north Korean issue is low. The US will not give up a toe hold so near china's capital, china will not give up the buffer zone in north Korea, and south Korea will not acquiesce to continued Chinese presence in north Korea after current north Korean regime collapses.
I think fall of north Korean regime will result in a much tensed standoff between the US and South Korea on one side, and china herself on the other.
The south Koreans will be tempted to gamble that if they attack the Chinese directly across the 38th parallel, the US will support them and eventually allow them to unify Korea by driving the Chinese out. The US will likely try to reign in south Korea to avoid an open war with china. China will gradually find it increasingly difficult to keep the peace in occupied north Korea due to a combination of south Korean agitation and the gradually realization, by the north Koreans, that while china can make their life better than it was under the Kim's, china does not have the power to make their lives as good as those in the south.
It will just be a dangerous, unstable flash point.