It may be more open to him returning, but if he doesn't return, it would be erroneous to say it's a plothole or that he didn't fulfill his purpose in the narrative.

Also, that's just your subjective opinion that character development trumps all. Fiction tends to lean heavily on it, because it can just make the shit up so that it fits neatly into arcs and whatnot. But there are amazing historical narratives that are completely devoid of any real character development. Often these stories are butchered by adaptations which attempt to tack a character driven story on to them.