Back in October, Patrick Dempsey teased that he had a conversation about returning for Scream 7 and claimed he was waiting on a script. Then in January it was revealed that he would not be returning and Joel McHale would be replacing him as a different character named Mark. Here's what Dempsey told Variety when asked why he is not returning:
“It just didn’t work out and we were dealing with the fires and everything that was going on and the schedule didn’t work out, unfortunately.”
Source: Variety