Toph's time to shine is over. She has taught Aang earthbending well, but now what? Will she continue to be a major character, or will she drop back into the shadows? She doesn't act as a mentor for Aang, that's Katara's job. She is not emotionally fixed on Aang, and that little "Oh Sokka, you saved me!" only lasted one episode. (The Serpants Pass) Katara is a major character, even after she finished teaching Aang waterbending, because she is a close friend (and possible romance) to Aang. The only role i see for Toph is groupie. (who can fight).