I haven't actually read the 'End of Ever After' novel specifically, but generally, it could be about the conclusion of a long - held state of 'ever after' like the end of a happily - ever - after scenario in a fairy - tale - like world. It might deal with the breakdown of an idyllic situation, perhaps due to some external force, internal conflict, or the passage of time.
There were 12 volumes of the novel, but only six or seven were actually published. There were two reasons for this. One theory was that because the publishing house had closed down, only six or seven physical books were published. Another theory was that the novel was finished, with only 12 volumes and no sequels. However, it was uncertain whether there would be a continuation or a final version after the 12th volume. Therefore, the specific reason was still unclear.
Since I don't have detailed knowledge of the 'after ever after novel', it could potentially be a fantasy novel where the heroes have saved the world from an evil force and now the story is about how the world is like in the aftermath. It might explore how the different species interact now that the threat is gone, how the political structure has changed, and how the individual characters grow and adapt to this new world. There could be new challenges that arise from the very solution that saved them in the first place, and the novel could be all about that exploration.
Since I haven't read the 'after ever after novel', the main characters could be a family. After a major upheaval in their lives, like the loss of a family member or a financial disaster, they each struggle in their own way. One might be a rebellious teen trying to break free from the new constraints, while another could be a parent trying to hold the family together. And there could be other characters around them who either help or hinder their journey in this 'after' phase.
One unique plot twist could be that Cinderella is actually a fairy in disguise. She has been testing the prince all along to see if he can love someone not just for their looks. Another could be that the stepmother has a change of heart after seeing Cinderella's kindness towards her own daughters. She then helps Cinderella get to the ball instead of trying to stop her.