"All mens souls are immortal, but the souls of the righteous are immortal and divine"
The Soul is the immortal immaterial essence of a being, e.g. Gods, Titans, Humans. The body may be destroyed, even the body of an Immortal, but the soul lives on always, and may return in a new form (Theseus returning as a God).
In "Immortals", the Gods are capable of "death", unlike in true mythology where they are not. But it is presumed they too do still live on elsewhere beyond this univeree in a higher plain of existence (perhaps with the "Deathless gods" in a spirit world such as Elysium with Chaos, Gaia, Tartarus and Eros being the first before Primordials and Titans).