Consider how powerful the Gem actually is regarding Granting a wish.. Can it do Time Travel..? As that is the current effect, travel back in time, a minute to several minutes ago, and intervene with a Featherfall effect on the body..
Maybe, in this case, due to being cursed, it takes the current dead body back with it.. and applies the effect.. so all they get is the still warm corpse... but the PC's wouldn't know what happened. Only that now two wishes were gone.. instead of one, as their memories may not have remained with the time jump.