It's amazing the number of people who can't think just a little bit ahead and realize one of the major reasons for boarding passes and seat assignments is the possibility of a plane crash. Because there's two possibilities...
One, where the FAA investigators have a list of people's names and what seats they were assigned, the seats have numbers engraved on them, and if lap belts were in effect generally still contain at least a torso. Meaning getting everyone's various bits and pieces back to their loved ones is a gruesome jigsaw puzzle, but a solvable one.
The other possibility is that the FAA investigators get a list of names of people who were /probably/ on the plane, a large field strewn with "loose meat and offal", and absolutely no good starting point. Also, a gigantic lawsuit and a moon-sized chunk of bad press as loved ones get the wrong body parts, or too many body parts, or too few body parts.
(BTW, never explain this to anyone who is currently on a plane.)