Now that we've established that Allison is almost definitely a witch, the end of the movie in which the spell book's eye pops back open makes a lot more sense. It was always the Sanderson sisters (Winifred in particular) who were needed to wake the spell book, so as a kid watching the movie it seems like the book waking up is a clear sign that the witches aren't actually gone. But given that Thackery's soul has finally been released, we can assume that the curse over him has been broken because the Sanderson sisters are, in fact, gone.
So how does the book wake up? For Allison, of course. She has, as we've established, been drawn to it throughout the whole movie. Even when she, Max, and Dani first entered the Sanderson home, she immediately went to the book (which, if it hadn't been behind glass, might have awakened to her voice at that very moment). The Sanderson sisters are certainly gone, but the end of Hocus Pocus isn't the end of witches in Salem.
