It is probably a bit of both. But agree with the deep rage. I get the sense there is a burning rage in all the characters, even Daryl I was suprised in one episode dropped hints that he might have some buried anger underneath his fun loving exterior. Nathanial I reckon will get really dark. I get the impression that…

Greg can't come back because he dealt with his underlying issues. That's really the theme of the show, all the characters have these buried issues. Greg finally faced his alcoholism so to come back would be a step back.