A better question would be what if the South outlawed slavery, and the horribly destructive Civil War had not happened? What technology advances would have happened without the burning of half the nation, the 750,000 dead, the countless wounded, and the numerous rapes? https://gettysburgcompiler.org/2015/10/05/finally-speaking-u... With the economic savings a nice check could have been cut to the Freedmen, and the co…
Could the US have done the same as Brazil. I don't think it was possible (except in a few special places like Appalachia and New Orleans and maybe the Eastern border states). The animosity over the issue had been building for 50+ years and was accompanied by a strong cultural divide and a slew of other issues that divided the US. And there was no regular tradition of manumission: black meant slave in the most of the South.
Maybe another 10 years would have made it possible, but I don't see where those 10 years could have come from.
I should add that victory at Gettysburg wouldn't have won anything but footwear for the rebels. Grant took Vicksburg and control of the Mississippi during Gettysburg, and in doing so fulfilled the Anaconda Plan. Grant and the Navy, historically a Northern/Midatlantic institution, effectively cut the South off from the outside world (except for the lucky blockade-runner and the small population of the Southern West. And the European powers had seen the writing on the wall like a year before. The CSA's slow death by privation was almost guaranteed. Even an Austerlitz-level victory at Gettysburg wouldn't have save the CSA. Washington was a fortress and there were of course Union reserves in the East and the possibility of transferring troops from other fronts. In my opinion, the CSA's two best chances for a negotiated victory were, one, a march on Washington right after the 1st Bull Run and two, a defensive or Fabian strategy maybe even coupled with asymmetric raids into the North until the 1864 elections and the defeat of Lincoln.