The roles that Ashley and Rhett play in Scarlett's life and heart mirror her place in the world, and her relationship towards the way of life that died with the war, and the one that followed after. Ashley represents the Old South, being the epitome of its virtues and its outlook on life. Rhett represents the new world that followed after the Reconstruction Era began, having far more modern values and viewpoints, including a far more modern opinion of women, their strengths, virtues and minds. Scarlett desperately wants to belong in the Antebellum life, clinging to it desperately, wishing that she could be a great lady like her mother was. But the truth is she belongs in the more modern era, having different viewpoints than those around her and standing out from the crowd because she cannot conform to the way they feel she ought to think and behave. Just as she pines for Ashley, but truly belongs with Rhett.
What drives Scarlett through the latter half of the book is the desperate need for monetary safety, having suffered the hardships not only of starvation and nearly losing Tara due to the high taxes, but having to take the full weight of responsibility for feeding and sheltering a large group of people, most of whom spend most of their time being ungrateful towards her. Only Melanie fully realizes what Scarlett goes through, and it deepens her love for her even more. This is what drives Melly to hold on to Scarlett and protect her throughout the rest of the novel, despite the bad things Scarlett does, because Melly alone (not even Rhett fully understands this, having not been there during the events at Tara) knows what shaped Scarlett into the person she is, and drives her to do the things she does.
The end of the book doesn't mention Wade and Ella but in only a few hours they lose the only two people that really cared about them: Melanie and Rhett.
And not long before that, they lost their little sister!
Likewise the fact that Scarlett simply left them behind at a hotel far away (as Melanie is dying), makes one wonder whether or not she abandoned them for good.
Had Dr. Meade been able to come and help Melanie deliver her baby after tending to the soldiers, she would have died for sure. As things were, she was left incredibly weak and frail after the long birth, and took many months to recover, nearly dying on the wagon on the way to Tara. When Scarlett saw Dr. Meade he had already tended to numerous soldiers and had their blood all over his clothes, his arms and hands, and even his beard. God only knows what bacteria he carried on him at that point, as dysentery was not the only illness that plagued the confederate army, and this was at a time when a doctor wouldn't give a thought to cleaning up between patients. He would have arrived to deliver Melly's baby with all that blood and all those germs still on him, giving her any number of infections, or "just" a general sepsis, any of which would have killed her for sure at that point.
And on a related note that's sadly very much Truth in Television - how many soldiers died during the American Civil War due to infections spread by hospital staff and in-field doctors?
Scarlett, and many others with her, judge Suellen pretty harshly during Gerald's funeral. And while Suellen is never described in very positive terms, except by Frank Kennedy and Will Benteen, when you think about it she must have been going through hell at that time in the book. Not only had she, just like everyone else in the South, lost her way of life, she had nearly died of Typhoid, lost her mother while she was ill, and had to starve for months after that. But then her older sister married her fiancé, which meant that she not only lost the man she had been in love with for years, but she had risked becoming an old maid, which she openly feared. But at the time of the funeral everyone was blaming her for the events that lead up to that (with good reason, but it's made clear that she feels very guilty over it). On top of that she had no choice but to marry Will Benteen, which did mean she wouldn't be an old maid, but she didn't love him and felt him beneath her social class. And as if to make matters worse, Scarlett shows up heavily pregnant with Frank Kennedy's child, truly rubbing salt in her wounds. Poor Sue might have been shallow, selfish and somewhat mean spirited, but then again so was Scarlett, and Sue definitely didn't have it easy.
Dilcey -Prissy's mother left out of the movie- is half native American. While never touched upon apart from her unique appearance, when you consider some natives were hostile...