Here's a description of one of the episodes that was never finished called "Simon Sez Doom:"
Mr. Elliot, Gaz's teacher, is running an orphanage care program. Zim joins it so as to take advantage of the game "Simon says" by telling the orphans to destroy the Earth. Dib joins the program to figure out what Zim's doing. He manages to save the city from the orphans, end the game of "Simon says" and almost blows up the orphanage by leaving the diaper-changing machine unattended.Unfortunately, Invader Zim as we all know it is forever lost. When asked if they would come back if the show ever came on air again, about half of the cast said no. Invader Zim would never be the same again, even if they did bring it back. So sad.