And more, poor put-upon readers.
The question was:
The tragedy of mortality — the tragedy gains poignance by the absence ?? of a well developed system of belief in afterlife.
There is an absence of exposition regarding the afterlife in the selections we read from the epic of Gilgamesh. That does not mean, however, that there was no “well developed system of belief in afterlife.” If that were the case, why would we read “and there was Erishkigal, Queen of the Underworld; and Belit-Sheri squatted in front of her, she who is recorder of the gods and keeps the book of death.”
In other versions, Enkidu had previously traveled to the underworld to retrieve some of Gilgamesh’s belongings. Other sources also state that Gilgamesh became a judge of the dead.
Gilgamesh does seem to have been struck by his own mortality after losing Enkidu, who was his match in all ways, his brother, lover, and comrade at arms. As he was two-thirds god and one-third man, to paraphrase the text, he may have thought he was immortal. Enkidu, having been made by a goddess rather than born, might have been expected to be immortal as well. The gods of the time aren’t necessarily immortal, though. They do not seem to die of illness, but they can be slain, as Enkidu and Gilgamesh killed Humbaba (who was a minor deity).
His grieving, like everything else he did, is carried out in an epic fashion. His reaction to everything has been to fight it, so his journey to find the only human he knows to have achieved immortality makes sense. First, though, he carried out rituals that, in that society, were intended to ensure the person in question a better life in the netherworld. Having a statue of Enkidu made served the same purpose. If Gilgamesh did not believe in an afterlife and have a fairly well-defined notion of what that afterlife entailed, the rituals and statue would not have been important.
As I noted in another post, any mention of a serpent in that society would be understood as a reference to the eternal feminine, the divine mother goddess. Gilgamesh’s loss of the plant that grants immortality to the serpent is likely a consequence of his earlier refusal to enter into the divine marriage with Ishtar, as was expected of any king.