The Dark Path
The Dark Path was the theocracy of Bandur Etrevion, which controlled most of the Kelfour's Landing region approximately six thousand years ago. It was a dark religion that was nominally in homage of the Empress Kadaena, with subtle references to the I.C.E. Age precursor of the goddess Eorgina (Orgiana). Its rituals were focused on everlasting existence, as well as various forms of demonic symbolism. The cult of Klysus (Luukos) was also annihilated in its consolidation of power. Uthex Kathiasas worked in the area when it was controlled by The Dark Path, implying that the hooded figures are surviving members. It was one of two major Unlife cults in the history of the region, the other being "The Iron Wind", who first started working there several thousand years later in the Third Era. Kadaena was known to have controlled this region in the distant past, so Bandur may have viewed his theocracy as revivalist. The Broken Lands portal was a relic from the Lords of Essaence.
While very little is established about the religion explicitly, the symbolism of The Graveyard seems to imply it was more of a false religion that mocked Eissa (Lorminstra). The juxtaposition with Kadaena was blasphemous, not something that made any inherent sense. The most plausible interpretation would be that the "Gates of Oblivion" were to be replaced with the forbidden "Gates of the Void", and so souls were to be "lost to the demonic" and quite possibly become demonic on other planes of existence. The "necropolis" implies that the city was to be replaced with a city of the undead, as well as the bodies of those who were unworthy of everlasting existence. While The Unlife is traditionally equated with the annihilation of existence in Shadow World, "going demonic" in Oblivion actually refers to the eternal peace of dissolving into total nothingness. The Graveyard inverts the symbolism of the darkness by allowing the struggle and suffering of life to continue forever in defiance of Death.
Behind the Scenes
"The Legend of the Necropolis of Etrevion" used some excerpts from Shadow World source books for the sake of proper titles. The "Dark Path" was probably based on the Shadow World Master Atlas, 1st Edition, description of using spells whose power comes from The Unlife: "In the process of learning an Evil list, there should be no question that the spell caster is turning to a new power source for his energies: the Unlife. Once the first spell is cast, he starts down a Dark Path. It may take years, but eventually he will reach the end: submission to utter and complete Evil." (capitalization in the original)
His book "Servants of the Shadow: Power through Thralldom" was another, more obviously borrowed phrase. (Kadaena is sometimes called "the Shadow" in the early books, in which she is sometimes spoken of metaphorically as the master, in a way that sounds like she is somehow still alive and behind the forces of darkness.) Several of the 1989 and 1990 adventure modules had a brief history section that included: "Great Demons were fashioned by the most powerful of the Lords who had fallen under the influence of the Unlife, led by the Empress Kadaena. Wise but twisted in spirit, the servants of the Shadow offered knowledge beyond that which the Loremasters deigned to give such 'lesser beings,' and the power of the Unlife grew unfettered in the Second Era."
This refers to the fact that most Loremasters were Iylari, and so were very patronizing of all other races. The Lords of Essaence were conflated with the Lords of Orhan (Liabo) in a typographical error from these paragraphs, which was intentionally preserved in the Legend, referring to Kadaena as the "first Lord of Orhan" when the two groups had nothing to do with each other. It might have been implying ascension along the same lines of the work of Eogun, the father of Kadaena's daughter who wished to make themselves into gods. While this would still make the statement false in the strict sense, in the Shadow World timeline the Lords of Orhan were unknown until 100,000 years after Kadaena, even though they were far more ancient. Kadaena would be "the first" known moon goddess. Something else to consider is that this actually one of two severe temporal anomalies written plainly into the story, where the Shadow Valley and Broken Lands spin-off stories have other temporal distortions. The paradox of Bandur pledging himself to a dead goddess but still owing his soul to her is central to interpreting it, rooted in the idea of undead demonic gods as sleeping toward a future rebirth beyond the pale.
In principle the soul of the Empress Kadaena would have gone to Eissa (Lorminstra), the goddess of death and rebirth, which is the root of his symbolic antagonism for them. The transformative nature of her perverse form of demonic rebirth, which is represented by her "grotesque" statue, is not immediately obvious but supported by extensive allusions to Lovecraft. However, her soul should have been absorbed by the Shadowstone, and destroyed when Ondoval took control of it. The theology that Bandur Etrevion and the Broken Lands are suggesting thus breaks with the Shadow World lore. The loophole in the source material would be that the Shadowstone had other unknown powers, and would intelligently adapt itself to the wearer, which potentially allows the contradiction to be avoided.
It is possible the Broken Lands solves this paradox with allusion to "The Shadow out of Time", implying Kadaena would survive death by possessing and swapping souls with others in the future who will die in the past. This is related to her "Guardian of the Forbidden" role in their theology as Purgatory, which is to say Oblivion, is characterized as a dream state of lost souls where time has no meaning. This story would explain how Bandur was acquiring dark knowledge from Kadaena, his unnatural scholastic proficiency, study of rare texts in libraries, inexplicable mastery of ancient magic such as their portals, obscure quests and monument construction, cults in his wake, nightmares, self-loathing, being driven to madness, acting out in fits of possession, and how his soul could have been owed to her. It is worth noting that "Kadaena Throk Farok" means "Guardian of the Forbidden", but the night-gaunts of the "peaks of Throk" who keep dreamers out of the underworld are represented by the vruul. The Lovecraft analog is Yog-Sothoth, who is coexistent with all spacetime and the guardian of all forbidden knowledge, who the dream-quest protagonist impresses but becomes trapped in an alien body.