The new economy
Certainly, with or without Lincoln being successful, slavery would have eventually been abolished or slowly died out. The Souths entire economy was based on slavery. If slavery was bound to come to an end at some point, would not that make the Souths's entire economy unsustainable? The South's economy as it is today is far more sustainable than when it was based on slavery. So while ending slavery had originally killed the Souths economy, was it worth gaining a new sustainable economy?