I think the fact there aren't any other metallurgists and it's a multi-national team means it's unlikely to be a purely professional matter as there's not likely to be any instances of research stolen or 'stolen', tenure positions grabbed etc.- though professional with some personal mixed in is quite feasible.
Would it be possible to have murdered him and then dumped the body outside? Lower gravity would mean it would be easier to move a corpse, but how much?
So far it's sounding very much like his "disappearance" is linked to some (attempted?) misbehaviour with women. Either by a woman he was trying to go too far with, or by someone disgusted by his behaviour (or a team of both of the above). Given how the base is described, it does sound like there's more than one person involved, even if only as accessory after the fact.