Remember Morgan from the very first episode of the Walking Dead. He was the first living person Rick, the main character, ran into when he woke up from his coma. Morgan was with his son hiding in a house. Eventually they split up as Rick went to search for his wife and child. We never saw Morgan again.
The actor who plays Morgan, Lennie James, told Digital Spy that the challenge of getting his character back into the Walking Dead has been a scheduling conflict. The producers check up on him every now and then to see what he's doing. The last time they called him he was busy shooting another movie.
I'm a little disappointed in hearing this news, because I don't think the reason to have a character in and out of a series should be based on whether the actor is free or not; it should be solely based on the story line. In other words, does it work?
He continues saying,
"It remains a possibility I could return. The character I played is away for a long time, so it's kind of up to them whether I stay away or if I come back."
He also explains that he had a great time on the pilot episode and was honored to have a whole scene with Rick alone.
They really need to work this out, but really think through whether the character Morgan truly has a place in the story, regardless of the actor's schedule.