Fuck that! Why is it, that in these stories, one victory is all it takes to turn back evil. Sometimes it works that way- rarely. More often, you have to heal, you have to rebuild.
That's what I like about the movie of The Neverending Story, because in fact, the hero loses when they win. The world was destroyed, and had to be rebuilt.
The problem with the traditional fantasy device is that it is an ending- I prefer tales that finish with a beginning. Part of the reason I like ol' Charles DeLint, usually, his stories end with a beginning, and sometimes, they pick up that beginning in a later tale.