We should all do all we can to ensure both mags are dead, 1 in a 1000 or 1 in a million it does not matter. One of my very best friends a very experienced pilot and engineer has recently been injured by a prop to the point of nearly not making it. So consider everything from a non pilot walking by and touching the prop to a tired after a long day engineer doing one last job.
There are not many situations where something like a prop is used or left unguarded