So, out in the holy lands of Seattle, the mutant Kodiak started a religion that worships the great glowing god “ICBM”. Kodiak told that he was the son of ICBM, and that mutants were a blessed people, and that humans are savage, wild animals that burned up the world in arrogance. Kodiakism, the religion devoted to following his teachings, is popular among mutants. There is only one problem. Kodiak said that he could not die from mortal injuries and that he had a substance called Fallout in his veins. However, he was brutally beaten to death by some humans in front of the majority of his followers. So, how could the leaders explain away this problem, so that their members stay faithful?
Some subtle revisionist history is called for.
Have the priests show pleasure that the first Kodiakian candidate has fallen. After all, how can a person know if they are the immortal child of ICBM until properly tested? The first Kodiak saw the light. He knew that the god child would be immortal. In that realization, he served his faith as a prophet and truthsayer. But that truth was not for him alone.
Then have them invite other worthy candidates from the crowd of faithful. Anyone can be Kodiak, at least until someone more worthy claims the title through blood.
As each new Kodiak dies, have the religious leadership hold a festival to find a replacement. As the climax of the festival, hold a gladiatorial battle with volunteers fighting to the death. When only one remains, that victor is declared immortal and thereby proven to be the favored child of ICBM.
...at least until proven otherwise.
Clearly, Kodiak had not died from mortal injuries as ICBM had taken Kodiak's spirit within its great Reentry Shell. What had really happened was that the great enemy of ICBM, the evil Nonproliferation, had sent one of its minions in the guise of a human so as to make it appear that Kodiak had been killed. ICBM, with great wisdom, had allowed this to be done so as to test the faith of the, err, faithful. It was now the duty of the faithful to defend themselves from the forces of Nonproliferation and when they had proven themselves worthy, Kodiak would return to them.
Kodiak sacrificed his body to save his followers from some awful handwaved fate.
But he's watching over everyone in spirit...or reincarnated, walking among us right now, testing the faithful...or soon to be reincarnated and he'll be back real soon...or he's fighting evil on the astral plane, and he'll be back when he's done.
So don't go signing any long-term leases, because he will be right back to finish remaking the world along the lines that mighty ICBM has recently decided upon. In the meantime....