Balderdash. The U.S. Supreme Court (sooner or later) would have issued a sane and Constitutional ruling which would have abolished Slavery and Involuntary Servitude throughout the entire United States and its territories—in stark contrast to the morally reprehensible, logically twisted, and patently unconstitutional Dred Scott decision.
Alternately or additionally, a Constitutional Amendment closely resembling the 13th Amendment would have eventually been ratified—starting with the North, but eventually with widespread support in both the South and the West—and the "Wheels of Progress" would cause America's "Original Sin" to inexorably fade into a shameful but distant memory...
Complete fantasy. It would have been an express constitutional amendment. The court cannot legislate. It cannot strike down a constitutional amendment.
To overturn the North’s slavery forever constitutional amendment, it would take 3/4s of the state’s ratifying it. There were 15 states that still had slavery at the time. Ergo it would have taken 45 states voting for a new amendment to overturn the Corwin Amendment. That’s 60 which is 10 more states than we have even today. Don’t even try to peddle some ridiculous fantasy about how a whole bunch of new states would have been created to pass that one amendment overturning the Corein Amendment.
There’s no way around it. The original 7 seceding states could have had slavery protected by express constitutional amendment had they been willing to accept that in exchange for staying in. They turned it down. Protection of slavery was obviously not the main concern of either side.