After all, all of the show started with Snow White and Charming's wedding. So, it seems like the show could end, but there is an opportuinity to begin another book, and another story.
There is a confirmation for a seventh season, so there has to be something to continue with.
Another thought that came to my mind, after watching episode 19 -The Black fairy, was the creepy similarity between the Black Fairy's moon mark on her wrist to Lily's star. It reaaly made me wonder why they ditcherd Lily's story. Could it be that the writer are planning to continue with it in another possible season??