OP, you shouldn't forget that no one is immortal, and we are going to die soon, and no one will live here forever. Nobody knows who is going to die next, and stop acting like you are in the better position to judge others, because your own judgment awaits you someday. Leo has done more good to the forum than you. You don't need to be happy over someone's departure from the world, this is how people will also be happy when you die.
I don't think it's appropriate neither efficient to tell to anyone that people will be happy when they'll die, even if they told it themselves to someone else, especially in such circumstances. Evilness doesn't cure evilness, it only spreads it more. Disturbed minds often legitimate retroactively their harmful actions by the punishment they receive. "Since people hurt me or wish to do it, I was right to hurt them." So if someone is mean, IMO we shouldn't stoop to their level and become like them, but rather stay true and upright to our ethics and lead by example.