There are rumors that Nergal eventually survived the cataclysm that should have been his doom. You might also check the following links for more information on the subject:
Nergal, along with Moloch and the Unnamed, were part of a tribe of Infernalists. They sacrificed humans into a well in the ground. An Antediluvian found them and, in a rage at the immaturity of their evil, proceeded to slaughter the tribe. He drained the three dry and cast them into their own well.
As the Antediluvian shed his blood into the well, that some might survive to learn his lesson, it was consumed by Nergal and the other two. After the Antediluvian left, the three emerged from the well as vampires.
Among his brethren, Nergal was the one most adept at dealing with other Cainites. It is said that he served as Arikel's wench, debated philosophy with Troile and traded vice secrets with the Tzimisce Antediluvian. He built himself a city on the Tigris, where he ruled as an unliving god, with a ghouled priesthood that would later form the D'habi Revenant line.
Nergal was, however, self-centered to a fault and assured of his own divinity. He desired to awaken the Sleepers his former tribe had kept asleep, to gain godlike power in the mortal plane. After demons told him that beneath his city, one of these creatures slept, he became determined to summon it and learn its True Name. To this end, he intended to sacrifice the population of Mashkan-shapir to a virulent disease that would shake the Sleeper from his dreams. His plan, however, was apparently foiled by his own priests, who betrayed Nergal's plans to Moloch, who ensured that the Cainites of the Second City learned of Nergal's plans. In the end, Lasombra priestesses summoned forgotten Abyss mysteries to plunge his temple into darkness and Nergal was thought to be destroyed.
However, it had been a ploy on Nergal's behalf, for he had fed the D'habi with his blood and spread them over the bloodline, assassinating those who would stand in his way if possible, while he himself returned to the original organ pit that had spawned him. After he had discerned that the resting place of the dark beast he sought to awaken was in northern Galilee, he reappeared, styling himself as Shaitan, the founder of the Baali Clan.
Constructing the fortress of Chorazin over the tomb of Namtaru, the Bringer of Plague, he managed to exvacate the dormant body and relocated it to Knossos in the Aegan Sea, constructing a great maze inspired by surface chasms and canals of the human brain. When reality itself warped around the island as Namtaru became more and more conscious, other vampires became alarmed and attacked Nergal in his stronghold. Together, the thirteen Clans caused the volcano beneath Knossos to erupt, sinking Namtaru beneath the sea and apparently destroying Nergal for good.
Rumors occasionally spread according to which Nergal survived and is still at large somewhere in the New World.
- Encyclopaedia Vampirica, p. 117-118, 150-151