How to be Deader than Dead
In progressive order of 'deadness':
What about copies of them still existing in entirely different parts of the Tegmark multiverse?
I rank "destroy their legacy" above "kill everyone who knew they existed" and above some relatives as well.
Religious participants, however, continued to ascribe less mind to the irretrievably unconscious David than they did to his buried corpse (-1.57 and 0.59).
That would suggest they should be supporting of euthanizing an irretrievably unconscious person so as to restore their mental capacities.
That would unquestionably activate their belief that this person is still alive and they would consider such an action to be murder. You could play their two beliefs "this person is alive -> don't murder them" and "at least as a soul instead of a vegetative patient this person would have some autonomy" off against each other but they would most likely back out of the conversation before any serious mind-changing happens.
It looks to me more like they rate the vegetable as more asleep. They think he's not conscious for now, but will be once he actually dies. I'd suggesting adding a part for asking people about someone who is asleep.
This seems like a very poorly designed study. Their metrics don't do a great job of measuring what they purport to measure. Even a dead person can "influence the outcome of events", albeit not actively. And besides, anyone who believes in an afterlife (or even really a soul) is likely to suggest that David can still "be aware of his environment, possess a personality and have emotions."
For your consideration, a psychology study as summarized by The Economist in "How dead is dead? Sometimes, those who have died seem more alive than those who have not":
The study is "More dead than dead: Perceptions of persons in the persistent vegetative state":
Ed Yong points to another interesting study, the 2004 "The natural emergence of reasoning about the afterlife as a developmental regularity":
Jach on Hacker News makes the obvious connection with cryonics; see also lukeprog's "Remind Physicalists They're Physicalists".