I honestly believe they won't kill Joel off. I believe Ellie goes on a rampage on some people and Joel will eventually stop her.Joel will be old in Part II, I can definitely see him die in this game, specially if they want to completely transform Ellie's character, which will fucking hurt because he's one of my favorite characters in video games.
Ellie will probably survive in this but die in Part III.
Other thing that can happen is Joel becomes the Joel at the beginning of TLOU1 which is smart and doesn't take unnecessary risks. If that happens, he might survive.
Uncharted 4 marketing tried to make it look like nathan drake will die or someone close to him and no one died. Different games yes but there's a reason they haven't revealed Joel yet. It's to make believe he's going to die.