The book ends with Rhett leaving Scarlett, and Scarlett deciding to go back to her family home at Tara to get herself together. She decides she'll head back there, and then:
With the spirit of her people who would not know defeat, even when it stared them in the fact, she raised her chin. She could get Rhett back. She knew she could. There had never been a man she couldn't get, once she set her mind upon him.
"I'll think of it tomorrow, at Tara. I can stand it then. Tomorrow, I'll think of some way to get him back." (63.135-136)
So, how are we supposed to take this? Scarlett says to herself that she's always gotten the men she's wanted, and she's right, more or less (she didn't marry Ashley, but he was still hers, kind of). So will she get Rhett back? Or is she deluding herself, lost in a dream of love and a future with Rhett as she was lost in a dream of love and a future with Ashley for the previous thousand or so pages?
There's no way to know really. One thing that is clear, though, is that Scarlett's gumption and determination is linked, throughout the book, to her willingness to push aside unpleasant thoughts. She's always determining to think about something tomorrow, refusing to deal with the bad things in order to move forward and survive. This is the root of all her successes; she was able to protect Tara, to own mills, to build her life up again after the war because she refused to look backward. She sets her eyes on a goal and she fights her way there, time and again.
But this is also the root of all her failures. Her refusal to really think through what she's doing once she's set her mind on a goal means that she never stopped to recalibrate whether she wanted Ashley the way she did way back when she was sixteen, nor did she ever consider whether she actually hated Melanie. She just kept tromping forward after her goals, never realizing she didn't really want to get to those goals in the first place.
The ending here can be seen, then, as pointing to a happy ending (she'll get Rhett) or as a sad ending demonstrating Scarlett's self-delusion (she thinks she'll get Rhett, but she won't). If the novel were to continue in the same vein, though, the ending wouldn't be happy or sad, but ominous. Scarlett gets what she wants, usually, only to discover she doesn't want it, and that she's made everyone miserable. If she sets her sights on Rhett, she'll probably get himâbut they'll both regret it.