One scenario might go as follows: Slavery has become so despised and denigrated that the South would cast about for alternatives. There were already many abolitionists in the South- some of them might have been run out of town, so to speak, but a significant number would come to power, I should think, that there would be heated debates all over the region.

As has been mentioned elsewhere, only the big landowners had slaves they depended upon economically and I can imagine the equivalent of the KKK nightriders making life difficult for them.

Interesting what ifs.