What irony can be found in Swan Necklace's death in the novel, Thunder Rolling in the Mountains?

Swan Necklace is described as believing that his guardian spirit protects him in battle, however he is nonetheless killed at the end of the book in an ironic twist of fate. The Blue Coats do not manage to kill him in battle, as ironically, it is during what is a peaceful journey for him and Sound of Running Feet that he is eventually betrayed and murdered by Charging Hawk, an Assiniboin warrior.