A couple of thoughts.

First, the oligarchy of the whites in the south survived for another 100 years thanks to the failure of the US govt to break up the plantations, implement "40 acres and a mule" and allow KKK/Jim Crow to rise up.

Second, there were numerous threats of secession from both the states in the north at times and the states in the south. Andrew Jackson, slave owner and racist himself, even threatened to come to the Carolinas and hang anyone advocating secession.

There were enough people who had the foresight to see that the nation needed to remain as ONE nation on this continent to keep it that way including Lincoln.

But..

Let's play alternative history. Suppose the north said "fine, become your own nation." It is my belief that we would STILL have come to war with the Confederacy at some point. The CSA was an expansionist government, eyeing Cuba, Brazil and parts of Mexico to expand their systems of slavery. At some point, as both separate nations expanded west, there was going to be a clash. The south wanted to maintain and expand slavery.