Showrunner Scott Dimple wants to make sure Morgan returns for season 5, telling Larry King:
I am so determined to make that happen by hook and by crook that I can say definitively 'yes.' But there's time and tide that can get in the way.
Norman Reedus says season 5 will be 'completely insane'
A bit. Those guys are very good at telling you a bunch of stuff, and you sit there for an hour and you walk away and go, 'What the hell did he just say? What's going on?' They're very good at masking what they want to tell you.
. . . From what I know, it's gonna be just completely insane. I sort of knew I needed like a good month to rest to jump in. The storyline they're throwing me is a thousand miles an hour.
While Robert Kirkman says that the villain Negan won't make the transition from page to TV screen soon, he does make it sound like we should be prepared for him to show up:
As far as Negan casting goes, [showrunner] Scott [Gimple] and I are always talking about who we would put in that, it's definitely on our minds, and there are definitely a lot of candidates. But I wouldn't expect Negan too terribly soon, although he is definitely in the plan. It's a 99% lock that he's going to be in the show eventually, so be on the lookout for that.
Kirkman also gave another vague answer about the state of the spinoff series:
As far as the spin-off goes, I'm actively working with [Showrunner] Dave Erickson on that, and we know when our proposed release date is — although I can't tell you that, obviously. We're working towards that show, and it's gonna be awesome.
Prep for the next season is already in full swing, with season 5 showing Rick and company recruiting allies to strike back at Terminus. Among the new recruits will be 17-year-old Burton, who will have already lost his leg when he's introduced.