It's very easy to say that the situation should have been handled peacefully and that the Civil War shouldn't have happened. That dodges the question of why the slave states would have wanted to participate in any scheme to abolish slavery, peaceful or otherwise. Slavery was their entire economy.
It's not like there weren't plenty of proposals at the time to deal with the problem. Lincoln himself was in favor of buying the slaves (it's up in the air if the federal government could have actually afforded this) and forcibly resettling them in Africa (ditto on the logistics here). But the fact is, any measure to end slavery would have required the cooperation of the slave states in Congress. And the slave-holding states did not want to end slavery. They had no economic reason to do so. Heck, they had every economic reason not to do so.
You cannot say this for certain because it didn't happen. For one thing more and more of the country was becoming anti slavery even in the south there were people speaking out against it. Also the plan to buy the slaves did not address the issue of replacing them as workers.
The end result of the civil war was a destroyed economy for the south that took well into the late 60 for it to start recovering from and a deep resentment towards those former slaves and the horrible Jim Crow laws.
Like I said if you look at how the end of slavery was handled in the Caribbean islands were it was phased out in steps you didn't see the issue we had here in America.
Just like in the alternative stories I have read where the south won the war have them having slavery today. Which makes little sense to me because it cost more money to feed, house and cloth a slave then it cost to buy a vacuum cleaner or to run a tractor.
Look at the fact that the huge servant population has disappeared except for the very wealthy.