Well, Milhouse dies to the standard tier 0 bullies that attack the protagonist and are used to show off the protagonist isn't trash anymore. Except in this case he still is. So Milhouse dies and the story is over very quickly.
he finds this worlds equivalent of Bart Simpson and dies directly afterwards to show how powerful Bart and his magic is. Bart becomes the new main character and slowly destroys the entire country while also pushing the local tavern keeper to the brink of madness.