I have enjoyed TWD on TV since it started and haven't been into the comic at all until recent (thanks Tom). With that TWD will stay the primary focus for my love of the shows, Fear I disliked at first, I absolutely hated Travis and half expected them to bring him back. I was amazed they nixxed Madison, but not ever actually showing her dead could mean they could bring her back in some mystical way. The hardest of the Fear deaths was Nick, I felt he was unkillable. But then they made Rick out to be very killable and then didn't kill him on the show. And yes, Alicia definitely needs an upgrade, I think give her a rocket launcher or a BFG3000. I am glad though they brought Morgan over and hope Dwight continues to shine with that ugly mug as well. I am concerned on what they will do when Michonne is done. Maybe they could put more focus on Negan and Judith?
Where I disagree with you is recasts, in normal comic universes yes you could recast them and move on. But when a character is done in TWD or Fear, they die (normally). And there is no coming back from that in this world. Unlike in the normal comic universe where death is reversible or they just simple reboot the universe.
I could see at some point if they rewrite/reboot TWD or if Kirkman writes a Fear comic series, then, a new show with new actors could be appropriate.
Maybe instead of bimonthly he does TWD and Fear monthly? Just stagger them appropriately. That would also allow for crossovers like they are doing in the show.
As for big screen movies. I wish the Rick movies would be big screen instead of made for TV AMC ones. He could do so much more that way and yes it could be rated R at that point.