He's a writer/producer who was credited as a co-writer on 4 episodes this season. Last season he was credited on none. He can simply step back and just be an actor in future seasons. Patton Oswalt is the narrator in an ABC show and will now be acting in an NBC show, so that shouldn't be an issue for Glenn either.
Writing credits are not a precise indicator of how much work someone does on a showespecially for a creator and EP like Howerton. The number of writing credits he has may vary but every season starts with he, Day and McElhenney in the writer's room with the other writers breaking each episode. Even if he didn't get a writing credit in season 11, he was in the room pitching, plotting out the season, figuring out episode ideas. (And using that he was only on 4 from this season's a pretty bad examplethat's a lot for a season of TV with a full writer's room.)
You're right, he could step back and just actbut he could also
not be able to do that. Oswalt's again a bad example because, like you say, he's a narrator. I bet he knocks out Goldbergs episodes 8 at a time in vo sessions that take a few hours. For Howerton to act full time on both the scheduling would have to be exactly perfect, and there's no guarantee that can happen. NBC's not gonna tailor their schedule for Howerton.
None of this means Howerton's definitely off the showthe pilot is still just a pilot! I'm not at all saying he's gone for good. I'm only repeating what Howerton's said: that there's a very real possibility he won't be involved in season 13.
They all have stuff going on. Dee has the mick, Charlie is in ton of movies, and Mac is about to direct the Minecraft movie. I'm sure they'll all make time for Sunny.
We've already talked a bunch about how The Mick is totally different
Charlie's not in a
ton of movies. On average he's in just over one a year, and a bunch of those are voice work. The shoot for a live-action feature can be pretty shortthe standard is 20-30 working days iirc or 1-2 months. A full season of television, (especially a network-length season) takes longer. (Plus remember these are filmed far in advance. e.g. Fist Fight shot in late 2015, before even season 11 had premiered.) In any case Charlie's the biggest star of the group and since these projects are built around him he has more freedom to adjust the schedule the way he wants. Howerton won't have that.
McElhenney's schedule is complicated to talk about considering we don't know that he's about to direct the Minecraft moviehe's hired for it, and it's dated for release in 2019, but there's no news about when they're going into production. Could be this year, sure. and maybe that's why they'll go on an extended hiatus, and maybe that'll make it so Howerton and McElhenney can both work on season 13. But maybe it won't work that way! That's literally all I'm saying, and it's literally all that the people who make the show have said: that there is a distinct possibility of Howerton leaving the show and/or there being an extended hiatus between 12 and 13