In an interview with Dan Harmon, he essentially stated that the season 3 ending montage was built to be the conclusion to the show. He already had an idea that he likely wouldn't be returning and was unsure about a 4th season, so he wanted to end it his way. Abed stepping into the Dreamatorium is essentially saying anything past that point, isn't his creation and therefore is being imagined (he states it symbolizes him leaving his creation). [url=http://collider.com/dan-harmon-community-season-4-chevy-chase/]Link[/url]