You are correct. If the Civil War had never happened slavery would have died its natural death within 15-20 years as it is a good deal cheaper to just pay some immigrant almost nothing to work than to purchase, feed, clothe and care for a slave.
The good example still exists today. Which would you rather do pay some paco $5 an hour to work or pay $10,000 for a slave and then have to clothe them, feed them take them to the doctor and make sure they can’t run off? Plus if they get sick and die or run off you are out $10,000. Its basically a terrible plan.
Which had been going on in North America for hundreds of years and which, in 1861, the Confederate leaders expected to continue for generations. They must not have thought it was all that terrible.
To this day, I've got to wonder what those nitwits who fired on Ft. Sumter were thinking when they launched that costly war.
Lincoln had actually proposed a very reasonable plan to buy the slaves from the sale of public land, an idea he'd borrowed from a minor party candidate for president in 1844. It would've been a whole lot cheaper than the war. The process would have accelerated after the price of slaves started to plummet.