Seriously? Turtledove?
I intended to leave the details of the victory open to discussion, but if you want a more concrete scenario just assume the CSA wins the same way it did in TL 191. It consists of the 11 states which historically formed the CSA, as well as Kentucky and the Indian Territory. It probably isn't a very likely scenario, but any sort of CSA victory is unlikely.
That's an Antietam Campaign with Lee (with 45,000 men) defeating McClellan (with 87,000) on the Susquehanna because - why, again? Why not dig in
east of the river to protect Harrisburg? Considering Lee has a) no supply line; and b) no bridging train; and c) is outnumbered almost 2-1, no, it's not very likely.
McClellan was a lot of things;
idiotic was not one of them. This is the same CG who managed Malvern Hill - or, at least, did not get in the way of Porter managing Malvern Hill. Same difference.
And this wins the rebels Kentucky and the Indian Territory, as well? Yeah, okay. Apparently Buell's and Grant's and Rosecrans' armies have vanished .. cripes, Halleck et al were at Corinth, Mississippi
five months before Antietam. How the hell does the Byzantine scholar justify that? Time travelers with machine guns?
This is why "save the webels" concepts are so entirely unpersuasive; they have to ignore the economic realities so hard, they may as well be grad students hoping for a tenure track position...
Anyway - questions:
1) If the Confederacy wins, would race relations in the north worsen, with many people blaming the blacks and republicans for the war? No; given the fantastical elements of any such "victory," presumably God would be blamed. Slightly more seriously, any surviving doughfaces after the great copperhead purge of 1862 would be blamed.
2) Or is there a chance that equal rights for blacks would be championed by the north, as a means of opposing the CSA? Yes; having a built-in guerilla movement in the enemy's camp is a godsend; likewise, it makes the issues clear to the Europeans who pride themselves on abolition.
3) Would there be treaties requiring fugitive slaves to be repatriated? No; why send useful manpower to one's enemy?
4) How long does slavery remain in the border states? Slavery was prohibited in the District of Columbia in 1862; Maryland prohibited slavery in 1864; Delaware, Missouri, and West Virginia in 1865. Kentucky, apparently, is magically transported into rebeldom, so they don't matter.
5) What happens to the abolitionist movement? It advocates for the destruction of the rebels and runs guns into Appalachia, across the Ohio, the Mississippi, etc.
Best,