There was not a single case were slavery died on it's own. In every instance it was ended through the actions of the government and in the face of strong opposition from the slave owners themselves. So if the south was willing to go to war to protect slavery from government action in 1860 then how long do you think it would have taken for such action to have been acceptable to the southern population?
Only two countries in the Western Hemisphere resorted to civil war to end slavery, Haiti and the United States of America. Lincoln's flawed statesmanship ("Gentlemen, what then of my tariff?") and that of various hotheads on both sides destroyed the Republic and impoverished half the nation for decades.
Without Lincoln, secession might not have happened and could quite possibly been reversed if it did. Slavery would have been ended within a generation or so without the deep and lasting hatreds that the War Between the States engendered.
Our ancestors should have done better.