(I must regrettably point out that most of my sources were lost in the CriticalHit purge)

In the fluff about the fall of the Eldar, it was stated that Slaanesh killed or devoured all the Eldar gods, save Khaine and Cegorach. Cegorach fled, and Khaine fought Slaanesh. Khorne, at least in the older fluff, wished to take advantage of this situation to devour Khaine, and so in the ensuing battle between Khorne and Slaanesh, Khaine escaped and dissovled into the Avatars we know and love.

So, if Khorne was powerful enough at the time to challenge Slaanesh and survive, and Slaanesh was powerful enough to wipe out the Eldar pantheon, wouldn't Khorne or one of the other two Chaos gods have been able to destroy the Eldar gods all along? And if so, why didn't they? Khorne certainly had the inclination to do so and a vested interest in one of the Eldar gods (Khaine).

In short, what was protecting the Eldar gods from Chaos before the Fall?