Fallout – Why are the bodies of the dead dwellers disappearing in Fallout Shelter

Dead dwellers disappear after 24 hours, so if you can raise enough caps to revive a large amount of them at once in less than a day, then it may be worthwhile. Just keep in mind that dwellers are very unhappy when they are around corpses. Reviving 52 dwellers would be a LOT of caps though, as they get more expensive the higher the level.

The only thing which could explain it (besides a bug) is that you may missing some electricity or water. If you haven't enough electricity your food and water supply will fall down and maybe collapse. This will increase the radiation of your dwellers. In some cases they may die on this.

Otherwise, I would say it could be a bug. I've had a situation which was nearly the same. In my case electricity was too low, which leads to the situation I described above.