I think they will need to establish more characters before killing anyone else off again. Tyrese is the only character to recently come into the permanent fold that I can recall. That Bob guy ain't gonna last. The little girl who shot that bitch is coming into her own (Carl, look out). Of course, I dont think we've seen the last of Carol before the end of the season.
So who's left?
Rick, Carl, Michonne, Daryl, Tyrese, Beth, Glenn, Maggie, the pre-teen girl, Carol (off on walkabout)
Did I miss anyone? I expect new characters first, before any of these die and I don't expect anyone to die until season finale. Although I'd hate for them to kill someone on that episode because then it would start to be predictable (just as it was predictable to me that Hershel would die in this episode)