He doesn't have to adjust too much. For him, he was gone only a matter of days, but ten years passed back here. The story was meant to be plot driven, but a couple of my characters, including the MC, don't have enough depth for even that type of tale. So that is something I will have to work on if I decide to finish this. However, adding conflict in via his dealing with a world that changed on him may be a way to do that. Thanks for posing the question that led to the suggestion.
I find my characters develop as I write about them they always will be a bit flat in the first draft. This wasn't so difficult because I started with two I knew well however they had aged a hundred and twenty years since I last wrote about them and still needed to get the hang of them.