He's stated clearly that he's out and done with Community, for the good of the show and his own mental health. And he's on to other projects. That's probably healthier than holding on to your baby, but then Harmon was treated like shit by the production company that owns the IP so it's not a similar situation to Veronica Mars.

http://danharmon.tumblr.com/post/23339272200/hey-did-i-miss-...