Honestly, I haven't read the comics, but I would like for Tyreese to show up. They already have an actor for him, so I know it will happen.
Clementine and Campman- I would like for Rick's group to encounter Clementine and Campman, maybe Campman can appear hostile and they Rescue Clem. Though I guess It'd be hard to find an actor to look exactly like Clem.
Molly - I think that if Christa and Omid don't show up, Molly would be a good replacement.
Lilly Caul (Video Game) - I would like her to get what she deserves. Maybe show up hostile like Campman.
Gary Taylor - Maybe so Rick could figure out about what happened in Dead Reckoning