I will note that in the world of Eska, Araushnee was not banished to the Abyss to become a demon lord, merely exiled from Arborea. The transformation into Lolth has not, but may yet still, happen.
To give credit where credit is due, they are:
Corellon Larethian Must Be Stopped
Why Did Araushnee/Lolth try to Kill Corellon?
The elves have ruled Eska for as long as anyone, including them, can remember. Legend tells that when they first came to these shores, it was a land teeming with orcs and goblins. A series of bloody wars lead to the complete annihilation of the orcs, and subjugation of the goblins.
After the elven nations had settled in and began to lead the idyllic lives they are commonly associated with, Araushnee, goddess of the dark elves insisted that at least some part of them must remain in a state of military preparedness to fend off any would-be attackers. Just because they had defeated Gruumsh and his orcs didn't mean that they could relax. There were other races who did not like the elves and envied what they had.
"The price of freedom is eternal vigilance," as it were. Corellon refused to allow her to keep her people, the dark elves, trained and threatened to erase them as a race if she did. So she trained them in private. When he discovered this, he rallied the other elves against Araushnee and her people and declared war, determined to hunt the dark elves and their goddess to extinction. Her people were better prepared for war, but they were outnumbered by a long shot.
At least, that is one version of the story.
Why would Araushnee, a goddess of fate, engage herself in a one-against-many war of the gods which she had no chance of winning? Surely the fate-goddess would back the winning team!
The fact of the matter is, Araushnee was - and still is - acting on the orders of Corellon, who she loves enough to suffer her current deformed and outcast state. The war with the dark elves, and their banishment, was an engineered event in order to imperil the elves and torture the mori’edhel.
Trapped beneath the earth's surface, the mori’edhel long for the sun and make the primary focus of their entire culture and lifestyle the redress of the injury that they suffer. Each and every mori’edhel’s entire miserable existence, they know, is the result of Corellon's decree; he is ultimately to blame for their current state, and so each and every dark elves’ life is, in a sense, a "sacrifice" to Corellon, who becomes the iconic focus of their immense hate and the ultimate author of their current misery and Araushnee’s encroaching madness. Araushnee makes her followers never lose sight of the "injustice" that Corellon inflicted on them.
But why would Corellon deliberately engender undying enmity for the elves? Without the orcs as foes, he felt the elves had grown complacent. Who stands to gain from endless attacks from external enemies, if not the god of protective warfare? Beset by deadly, implacable foes, the elves must pray ever-harder to Corellon for his protection. They are most useful to him when they are imperiled - indeed, as a dwindling people, obsessed with their past glories and the great deeds of their race, they are most valuable to Corellon, as their entire energies are focused on the preservation of their magics (of which he is the patron) and arts (of which he is the patron) and the defense of their remaining communities (of which he is the patron) against their dark elf enemies (for whom he is responsible and from whom he draws yet more power).