Well, the rules for the weapon simply state that if you score a hit, the model must pass a Leadership test or they get removed from the tabletop.
The only mention the Blade of Realities has in the FAQ's is talking about whether a similar effect (a leadership penalty from a spell) would assist. The answer was no. Therefore, I'd conclude that you can't affect the outcome of the Leadership test either way. You just roll to hit, if you score a hit they take a normal Leadership test on their own Leadership, and if they fail they die with no saves of any kind.