Longer than four years.
EDIT: Pithy response already taken. However, had the Confederates not been rash, aggressive and injudicious, they could have fought out the battle of slave vs. free for many, many years to come. The whole point of the United States political system is to restrain and delay action: using levers of power (e.g. the Supreme Court) could have thwarted any attempt to abolish slavery for decades if not altogether. Instead, provoked by a threat that Lincoln's own words show wasn't there, the Confederacy threw the dice and lost. Had they won, their opinion of the fighting qualities of the Union would not have improved.
But the big point being missed here is that it doesn't even have to be up to the Confederacy to start another war. If domestic opinion in the North goes the right way, the South might become the most pacifist nation on earth and still have a war forced upon it.
Certainly.
Most likely over territories in the west. I could certainly see an US that decides that they don't want the CSA to have access to the Pacific.
But then again, I could see a US that wouldn't really care if the CSA tried to get access to the Pacific.
Could go either way.
I voted possible but unlikely in the poll.