I've been reading all kinds of fantastical theories, but really the movie is not that deep. That all the characters except Tony/Edward were manifestations of Susuan's persona, that he had cancer, committed suicide, so on and so on.
What I gathered from the film was that Susan now at a low point in her life, in a loveless marriage where she is being cheated on by her husband, Hutton ( good luck getting a man that good looking to be faithful ) her work is passionless and mundane, she is surrounded by the fake, the processed, sleep deprived, utterly miserable, and isolated.
The novel served as a simple "look I did it, proved you wrong" showing to her that he could write a novel, however he attained the necessary particulars through extreme pain and loss. One of the themes of the film was that Susan was not truly a creative, she knew this later in her life.
Edward's novel, and standing her up at the restaurant did two things.

1. Left her, and compounded the reality, alone and broken, just as she had left him.
2. Will now brand her with so much hurt, it will give life to her art.