I've just finished rereading the original Citadel game, and I thought I might lay down how I plan to approach players going inactive. If a player quits or disappears and doesn't seem to be coming back, I will remove them from the game. No need to sacrifice them. If they were Evil or some other key role and I think it's going to seriously mess up the balance, I may retcon someone as a Sleeper Agent to take their place. I'm not expecting it to be a problem, though. The Ruins game had a pretty excellent participation level from almost everyone involved.