Actually I think that regardless of the length of the civil war, slavery would die off after the war ended if only because of the trouble it caused.
Perhaps the border states, and depending on butterflies some states that may leave the CSA, and rejoin the Union are allowed to keep slavery. West Virginia may stay as part of Virginia. Abraham Lincoln will likely stay alive to oversee reconstruction, as the South's without its otl victorys, that made it appear that it had a chance of victory, will not have that many people looking for revenge against Lincoln (and even fewer willing to care it out.)