Engineers know to build in redundancies when lives depend not necessarily exact replicas of the primary unit but systems whose secondary function is to carry the load when a primary system fails. The principle applies to all organisms and the inanimate objects designed to support them. But the sun and the rock that is earth need no redundancies. Burning, cooling one of each, they disintegrate without feeling for the mantle or the planets.
Some individuals may, it turns out, be irreplaceable. There is not always another girl singer this one is the only one for us at this time, while we're alive in this place with the random weather. The one singer, leader the one who interprets God's words when she is assassinated, terminated, released we are not released, velocity registers a mandatory, momentarily momentous palpitation that is gone unlike Shakespeare so far. She was not the sun. But she was found to be irreplaceable, unique her song.