From normblog reader Noga, another contribution to the discussion started by this post:
It is possible that Austen might have toyed with a different ending but she wouldn't have been Jane if she had succumbed to the temptation of crediting Crawford with the ability to change through the power of love. She was probably the wisest of persons, and she knew that a skirt chaser simply cannot change himself, however fervently he may wish to or delude himself that he is able to. Married to him, Fanny might have had a more interesting, glamorous life but she was never interested in any of this. She was that literarily boring creature, a truly good woman for whom principle mattered. Edmund was the only one who could match her longing for a fair, just and modest existence.I believe Austen had a special affection for her. I can't recall anywhere else where she intervenes on behalf of her protagonist the way she did in this novel, when she says in the last chapter: 'My Fanny, indeed, at this very time, I have the satisfaction of knowing, must have been happy in spite of everything.'
It is said that the sparkling Elizabeth Bennet was Austen's alter-ego. If so, then Fanny could be regarded as her daughter. For what does a mother wish for her daughter more than anything (that's aside from a brilliant career these days)? The knowledge that she is loved and safe with a worthy man. Fanny, it is interesting to note, has no mother (to speak of), unlike, for example, Marianne from Sense and Sensibility, who has a loving mother who cares for her.