Cassian dies before the blast hits; she hears him exhale and not inhale again, feels him slump. She's relieved, and lonely, but it won't be for long.
He is the last to go. She felt Chirrut die, fiercely content, and Baze, heartbroken, and Bodhi, terrified and elated, and the others she led there without knowing their names, one after another. She is left to see death swallowing the sea, to turn off the lights as they all leave. Her lifetime of loose ends, all tied up at once.
Jyn looks up, and smiles, and blinks - and the world ends.