Thank you Shadow Knight.
I imagine now that I've had some more time to think about it that Davis being Davis he would probably have scattered Confederate forces to the point where the Confederacy [Save the Western States and Territories (Texas, the Indian Territory, and Western Louisiana)] would have collapsed within weeks (or a few months-the Confederacy hasn't undergone the Winter of 64-65), but they HAVE lost all their ports much more quickly. The permanent losses of the Shenandoah, Goldsborough, and Wilmington NC so much earlier ITTL will be critical.
The status of the average Confederate in terms of standard-of-living won't be as soul crushing ITTL as IOTL. But they'll also be without as much bragging rights either. Holding out for two years isn't quite the same as four. The War has ended with Lee's Surrender, in battle, as most will see it, not with a whimpering occupation of Richmond before an overwhelming Yankee Horde.
IOW, Davis sends just enough troops everywhere for them to be decently beaten (defeated in detail), and that's it. Distance and the decrepit state of Confederate railroads (1) will bar any "Rapid Deployment Confederate Force" getting to Virginia or even the Tideland States in time.
1) Different rail gauges, and whole cities being bypassed by the Southern rail network in order to promote King Cotton over industrial, civilian, or communication needs.
Postwar? Either very bright or very dark. It depends on the intangibles of Lincoln's survival and how long Reconstruction can be maintained. If Lincoln is still alive in 1876 (BIG if!), and with an early end to the war (2) he may not become so aged, it's doubtful the GOP's most popular member would have allowed someone like Rutherford B. Hayes to be the nominee, or that Thaddeus Stevens would have enjoyed filling the power vacuum left by Lincoln's assassination.
So, I'm just exercising Author's Preference to say that on a particular night in Ford's Theater Ulysses S. Grant ACCEPTS Lincoln's offer to attend (Julia Dent Grant is much more smug dealing with Mary Todd Lincoln with General Grant's unblemished record), without Julia's objection. Since Grant has a full military escort wherever he goes...
Either Booth/Assassin X is caught or killed, or the would be assassin is frightened off and eventually drinks himself to death. End result? Lincoln gets himself a "Secret Service" 1860s style whether he wants it or not. Pinkertons, probably. So Lincoln can't order away his military guards.
2) Fewer dead, wounded, and the nation as a whole is not as exhausted. By two full less years of Total War.
It would take a Gilded Age historian to speculate what might happen in a Post-Grant Presidency ATL where the war effectively ended after Gettysburg and Lincoln had not been assassinated. I lack the knowledge to do any such speculation.