This is a classic case of "Will there be a sequel?" (There's not, unfortunately.) Although the witches of England are defeated in The Witches, there is still a world full of them left to conquer. We almost have a happily ever after, but not quite.
For a brief moment, this makes the triumph over the English witches seem a little less climactic. The narrator himself realizes this, too: "'Oh no!' I cried. 'That means everything we did was for nothing!'" (22.8). But, the ending of this book shows the narrator and his grandmother setting out on their plan to finish off the rest of the world's witches, and Shmoop, for one, anticipates victory. What do you think? Will they succeed?