Unfortunately, the Null were not lying when they said that they had a way to assure the deaths of the victims. Fake deaths would be seen through, and if this was attempted, they would likely immediately call Rey- and anyone else who attempted it- out and consider them enemies of the Null. We love this idea and we wish that it could have some kind of payoff, but due to other factors at work, the Null just ultimately would not be fooled.