Highly speculative. Keep in mind that the South didn't just keep slavery alive because of rational, economic motives but also because it formed the basis of their entire social system. That's why even poor whites who didn't own slaves supported the system - it gave them a place in society that wasn't at the bottom of the heap. Really, belief in slavery constituted an ideology, and people will defend ideologies even when their rational basis has been eclipsed.
OTOH, the ideology of Northerners - either abolitionist, or the many folks who simply believed in America and its great shining future, and didn't care one way or the other about slavery - could be just as merciless and uncompromising. The Civil War was a clash of ideologies, like WWII or the Cold War, and that kind of fight can become pretty horrible, because ideologies encourage people to believe anything is justified, because they are Right with a capital R.
The more I read about the Civil War, the more I'm grateful that Americans aren't remotely like that anymore. All the partisan nonsense going on now is merely a dim echo of what went on then.
And Europeans looooved that steady supply of cotton that supported their huge textile industries. Europe's elite classes were more sympatico with the Southern "artistocracy" than crass money-grubbing Yankees. No telling how they really would have factored into things.
So getting back to the topic at hand, the whole vampire metaphor is fun but extremely limited in how enlightening it is. What would be even more fun is to have someone tell the full and truthful story about the Civil War. It would be wild, hairy and incredibly dramatic. I keep hoping for a TV series on the topic, something that is brave enough not to just stick to Grant did this, and Lee did that, and it was all about armies maneuvering in the fields. Boooooring!