According to Screenrant.com and tv line... Glen Mazzara has mentioned that he's going to try to stay as close to the source material as possible this season. A few of the Survivors will NOT be making it out of the prison. Below is an excerpt from the screenrant.com article:
“There’s no place we won’t go. Everything is on the table. This is a cutting edge cable drama. I’m comfortable with that material and we answered a lot of these questions on say the Shield and when I worked there, so I’m comfortable dealing with very, very edgy material. That being said, you want to make sure that things are not gratuitous, that things are not offensive for the sake of being offensive. I don’t ever want the show to get too bleak. I think we’ve done a good job of creating characters that people care about. I think there’s a heart to the show.”
To read more involving the season 3 spoilers, which aren't much of spoilers but will quench your thirst for now, head on over to screenrant at the source link below.
I'm not sure if this has been posted already, I don't believe it has, but I could be wrong.
Update: Speculation on celebdirtylaundry.com says that 1 of the characters to die may be either Lori or Glenn. As we see in a preview of next week's episode we see a grave with a cross on it, probably dug by the survivors at the prison for the burial of a friend. It's currently just speculation as to who's grave it is but in the comics we know that Lori dies, and last week we saw Hershel bitten and his leg violently amputated with an ax by Rick.