In many cultures, isn't the rule that the body has to be dead for a certain length of time for the soul to depart?

I know the reality is finding the right time between being absolutely certain someone's dead (not in a state that just looks dead) and having them be a rotting corpse, but we don't know what the "reality" is in this construct.

They made a point of showing Ruby coming back in a "dead" body instead of just showing up at Sam's door with a death certificate (which she wouldn't be able to get anyway), so I'm assuming they did this to push the "Ruby's good, we promise!" agenda.