Godi Death

Godi Death [GOH-dee deth] is a term that refers to the transmutation of god-souls. A god cannot be killed, but they can give up their physical spirit and create an intellectual life form. Every planet with intelligent life is the result of a Godi Death.

Noteworthy Examples
Yisa, Tzad's mother, achieved Godi Death by turning into life on planet Earth.

It is possible the Helura is missing because she achieved Godi Death, but there a many flaws with that theory.