I've lost friends. I've lost friends I've gamed with. There are many memories that I have of those games, and their characters, and every time I tell those stories to someone, I feel like I've shared a little bit of the light those dear departed have given me. I don't know that I could pull off using their character as a 'main' character, but perhaps I could manage to swing bringing that character in as someone that the main characters encounter.
Of course, you may find that character takes on a life of its own, once you drop it into your story. If so, take it as a 'vote of approval'. I know I would.