Kirkman indicated in the letters section of issue 99 (or maybe 98) that neither Merle or Daryl Dixon would be showing up in the comic in the near future.
I'm not hopeless. Kirkman often says one thing and does another in an effort to keep readers surprised. I imagine that we still may see the Dixon brothers in the pages of the comic. They are increasingly popular, getting their own videogame and AMC may demand that they appear in the comic. Alternatively, Kirkman's contract with AMC may be the reason why Daryl and Merle won't ever appear in the comic. I guess only time will tell.
I would hope that, if AMC "demanded" Kirkman do something to a property that he created and has had sole control of since Day 1, he would tell them where to stick their demands.