There would have been no more story if Rhett had given a dam. They would have reconciled and lived happily ever after. Isn’t that what we want, according to Michael R [whose writing course we looked at]?
Well no, not in this case. We leave Scarlett collapsed on her staircase, but with somewhere still to go tomorrow, She’s a resourceful bitch, she’ll figure it out. And besides, I think we all know he really does give a damn, he’s never going to get Scarlett out of his system. But he has to storm off just at that pointy, so the story goes on working in our minds after we leave the cinema or close the book. (Yes, I did both in my time.) Part of the fascination is wondering what Scarlett will get up to next.
Also Rhett has to be a strong character; he can’t just succumb weakly. If he had given a damn, he wouldn’t be the same old swashbuckling, roguish Rhett, Not a very nice person, really. If he had not given a damn, neither would I. As it is, we care very much that Scarlett, having finally seen the light, is left on her own to nut it all out again.