No more Jack?

Would Lost really kill off Jack? One of the reasons I love this show is it's willingness to do almost anything, but I wonder whether the producers would willingly go that far. (Granted, if Matthew Fox bolts to do more movies, there really isn't much they could do to prevent it.)

As I've previously mentioned, my wife and I have an "untouchables" theory regarding Jack, Kate, Sawyer and Locke, meaning that the show will never get rid of these characters. That theory can't cover when stars decide to get out while the show is in its prime, though, so we'll have to wait and see.

Maybe all of this is one reason why the producers awkwardly introduced two new cast members at the beginning of this season by pretending that they had been part of the crash survivors all along. Note to the producers: If Fox or anyone else leaves, please do kill them off or somehow explain their absences. Don't recast the roles. (I don't really think they're that foolish, but it has crossed my mind.)