If either the Civil War ended in a peace treaty that recognizes the CSA as sovereign state or if Lincoln and Republicans never really moved to abolish slavery after the war. If not outlawed in 1865, how long do you think slavery would have persisted in the South? Into the 20th century? It's actually crazy to think about slavery being around for several more decades.
I think it could have lasted into the progressive era from ca. 1900 to 1920. So similar to when child labor was officially banned in the US.
Until there's another war and they get invaded by someone else. Or they just rename slavery something else. They saw slavery as a core belief sanctioned by God.