You know, one thing that strikes me about the south is that we in the 21st Century hate their ideology and therefore assume they would not evolve. Look at how the American Revolutionary history how the essentially "Confederate" Confederation Continental Congress which fought in defense of weak government was creating the strong central government under the U.S. Constitution.
It happened because the founding fathers essentially "Wised Up", learned from their mistakes, and learned to make things work. I see no reason that the Confederates would be simularly shackled. They had men of talent, like Breckenridge and Benjamin. Among the "next generation" they had people like E. Porter Alexander, Mosby, Cleburne and others.
And I think with the common history, gradual Emancipation starting in the 1880's, industrialization (part of the change in ideology) could make the South a better place than the very low expectations I see routinely on the boards. I'm not saying would be great, but better.
And no, with their own sense of legacy, I never see them rejoining the US.
You're more hopeful on the CS than most scenarios I see on AH.com, which boil down to:
1. The US is angry at the CS and reconquers part or all of the CS within 10-40 years
2. Without the CS, the US goes socialist/communist
3. Without the US, the CS goes military dictatorship/unstable banana republic/falls apart
4. The CS limps along and is still either racist, segregated, or has slavery/sharecropping into the late 20th/early 21st century
5. The CS never changes and is an international pariah and falls apart.
6. Without the US, the CS remains racist/segregated/unstated racist/slaveholding; if they're so Christian in the south, then they should eventually realize the error of racism/slavery.
The unspoken question is, what if they change? What if they realize their error and sin and emancipate and grant civil rights? What if, without OTL Reconstruction and the sour grapes it likely engendered, they make changes on their own? That could be explored in a timeline somewhere if someone has the time/inclination to do so.
Sorry to post here; I normally avoid anything CSA on AH.com because it's a powder keg for some people if you sneeze in the wrong direction. (That was sarcasm).