From what I have read, Lincoln's plan for reconstruction was much more about reconciliation that the plan that was followed by the controlling faction of Republicans after his death. That plan had little in the way of reconciliation. Lincoln considered himself as president of the nation which included the south. Having read some eyewitness accounts by southern soldiers of the surrender at Appomatox, the procedure was conducted with dignity and respect and, here I am assuming, met with the approval of Lincoln if not directed by him. Reconstruction was a horror and conducted with malice and if we are not still paying the price, we still see the effects. There are historians who believe that Lincoln would have done things differently. At this point we will never know for certain.

As for slavery being on its last legs, there was a concerted effort among southern slaveholders to push slave holding into new territory and the slave holders were the most powerful element in southern society. I am still amazed at how people will follow the elite possessing wealth and influence with their tails dragging behind them even when it does not serve their own best interest. But even the non-slaveholders in the south were accustomed to an economy based upon the plantation and driven by slave labor. I do think that eventually slave holding would have diminished and faded, but it may well have taken three or four more decades or more and there would have bitter opposition to its ending even then.