Patrick Dempsey is listed in several current cast lists as a participant in Scream 4, but it’s no fact, Jack. As we understand it, what happened was: his name slipped into a cast list that went out with some of those third-party calls for Scream 4 extras, giving it a sense of officialism. But it was very likely a mistake attributed to someone needing to put together some quick copy and doing the math that Mark Kincaid is part of the continuing prime cast because he survived Scream 3. Or, since Dempsey is bankable business nowadays due to his gig on a little show called Grey’s Anatomy, it’s just assumed he’ll be part of this.
We imagine Kevin Williamson is doing quite a lot of juggling in the story – his beloved characters from the original trilogy co-mingling with his next generation of self-aware smart-asses. To try and shoehorn in a character introduced in the chapter he didn’t write might be stretching it. The good Detective has no link to Woodsboro like the rest of the gang do – he’s too busy catching criminals on Rodeo Drive.