OK I think you peoples need some staightening out.
originally there were a bunch of gods, Asuryan being the formost. Sadly, all of them were weakened in the war khaine waged against the rest, so when slaanesh (the embodiement of all bad qualities of Eldar) waoke up, she (yes slaanesh IS a she it states it in the Eldar codex) kills all of them 'cept khaine & Cregorach. Khaine (for a change) protects the Eldar stopping she who thirsts (for some reason people keep refering to her as he-who-must-not-be-named, that was Voldemort from hairy potter series) but is splintered into tiny pieces which grow into avatars. Cregorach ran away & hid. So there are 2 still alive. 1 in fragments, and one in hiding in the webway.
Ynnead:
As far as I can tell, Ynnead is formed of the souls of all Eldar,y'know Exodite world spirits craftworld infinity circuits, Harly souls... yep you get it. Anywho when Rhana Dandra happens, to my understanding Ynnead is still asleep. The pheonix lords lay down their lives to stop chaos, and as Fuegan (the last one) dies, his soul completes Ynnead. Then Ynnead wakes up. You thought Slaanesh was bad. Wait till you see what Ynnead does. So much for Slaanesh. (from here on this is my own telepathic futurscrying abilities)So anyway, some serious chaos but whippin ensues. So chaos is gone. Then some corrupted marine guy goes and starts being evil. he recruits evil marines and stuff happens- the cycle goes again. he restarts Chaos, gets them deamons back y'know the works. so it happens again. by my logic this should be around 7th edition. Anyway, now you are enlightened. Don't question the prophesies.