When somebody has died, we encourage adding a little prepositional phrase to the beginning of our wish. The phrase that I use is "If rebirth is true, may so and so..." and I give exactly the same wish. Now, I personally don't know that rebirth is true. Buddhism teaches it, and if it is true then they're now reborn, in another body somewhere. It might be in an human embryo, a higher or lower realm of existence, whatever Buddhism teaches. As I don't personally know, I just add a phrase in the beginning, "If rebirth is true..." Then I feel I'm wishing them the same sort of wish I would if they were still alive here and I could see them.