Let ne tell you what I used to tell my students when this question would always up with Lincoln's inauguration, much to the stupefaction of my northern students. Now, of course I know what the cost of the war would be, and it was a terrible price to pay for the continuation of an intact Union, and I would not have asked America to pay it, had I known what it would be. To avoid some of the future antagonism between the USA and the CSA I would have been as generous as the Northern people would have allowed, and in March of 1861 I think they might have allowed a good deal. I would have met with Jeff Davis, invited him to Washington, or gone myself to Montgomery. I would say that, although our only real difference was the extension of slavery, not its existence, I would agree to the separation of the CSA (and remember this is before Sumter, so it's not 11 seceding states). You can have Sumter, your independence, a portion of the western territories, say New Mexico and Arizona and our blessings for a bright future. The US Post Office will delver your mail until you have your own postal system set up. The US Army will keep troops on your Indian frontier until you can take over there. The USN will defend your maritime interests until you have built your own navy. In return we ask for free navigation of the lower Mississippi and you will have the similar for the upper portion. We offer a free trade agreement and an open borders policy for your people. You get the idea. Make it very easy to separate and you make it easy to reintegrate the states. Assuming, though, that the Southern states decide to stay out of the Union, what of slavery? Yes, it will continue for decades, and in the border states as well, but I doubt very long into the 20th Century in either section. Perhaps a slow morphing from chattel slavery to peonage to second class citizenship to eventual full citizenship rights,and perhaps also a less rancorous adjustment from servitude to freedom in the process. Pie in the sky, Cloud Cuckoo Land, will of the wisp mental meandering? Perhaps but the price was some 700,000 Americans, and remember Confederates were Americans, too, but at that price I'd have left the South go. Britain survived the loss of her American Colonies and did just fine shortly after the loss and there is little reason to think the US would have come to a bad end from letting the deep South go. Yes, it would be a different America today, but not necessarily a bad one for either section.