does it tell you something if they sink or float when they die? i only ask because im cycling my tank and have had them do both. and i had 3 completely dissappear. i dont even know where they could have gone but no where in or around my tank
usually they will sink. if they died from a swim bladder problem or have been dead in the tank too long they will float. missing fish will either be on the floor, in the filter, eaten by other fish, or stuck inside whichever decoration you've already checked 3 times.
you're cycling with fish? are you testing the water and doing changes every day to keep ammonia and nitrite in check?