We know that Kirkman often brings characters in the story that serve one basic reason for that particular moment in the story and after that often are seldom (if ever) seen or heard from again.
So what characters can you think of that are technically still alive in the comic but most likely will never be seen again.
THe one that comes to my mind is Anna. The girl that gave Carl the note way back in issue 129. Looking back at it now its easy to see that Anna's purpose was simply to foreshadow Carl's future girl trouble storylines. But it is funny how the character seems to have literally dropped off the face of the earth.
Supposedly (at least according to this wiki) it says she appeared in issue 144 but I don't remember seeing her and there is no image of her uploaded to the site for that issue. It also says she was on the cover of issue 157 and while Annie is definitely on the cover I don't see Anna. I think the person that said that just confused Annie with Anna or was trying to say that that nameless young girl on the cover was Anna.