Gengar rn is a lot stronger than it was as cursed body is another layer of RNG which can define a match late game. So no levitate existing wouldnt make him better by any means. Levitate was removed cause mmo follows the latest generation changes, and in gen8+ there is no levitate gengar, its that simple. So no, it wont return, and its not needed at all, gengar is frail by default if you look at his defensive stats and typing.