I can accept it because it's the PoD, but I do not believe Lincoln would have surrendered Fort Sumter and his entire political position re secession without extremely dramatic changes to his personality. As is emphasized by what happens in your TL, there's really nothing to negotiate: either the South is independent or it isn't, and they aren't going to accept the latter.
Aside from the implausible PoD, I like the story.[/QUOTE
At the time, everyone, including Lincoln, thought this would be a short, quick war, and the South would back down and the Union would be saved. The war was not initially fought with the idea of 600,000 deaths and more than a million maimed. In my story, Lincoln relives what really happens in his sleep. Lincoln, being a strong, independent leader, has the courage to change course and live with the consequences.
With regard to Ft. Sumter, there was a split in his Cabinet -- General Scott recommended against defending the fort for tactical reasons.