I was just reading the Scream 3 wiki and Kevin Williamson - who wrote OG Scream and Scream 2 - had an outline for Scream 3 but he was unable to return to write it so the studio hired someone else, who went in a completely different direction.
Originally, Scream 3 was to return to Woodsboro and the killers were all kids who were fans of Stab. The final twist "of the movie was when Sidney walked into the house after Ghostface had killed everyone ... and they all rose up. None of them were actually dead and they'd planned the whole thing."
god! I’ve got to say I prefer that to what we actually got