or if you want a death massage out of vanilla you can also get a game value, and in event values there is death massage, you could use it as a death massage, but i would do it fancyer by doing set var text, do completeDeathMassage in the chest, a text that has &4 or whatever you want it for a color to be, and after that the game value in the chest. Than send Massage all players and the var completeDeathMassage. That would do that always when a player dies (if you put it in player event death) than the vanilla massage would pop up in chat.
NOTE: For it to do it with all death do it in the player event death, and player kill player event