I don't believe it would be written in any fluff related to eldar or even in the recent codex, but would eldar Exodites require spirit stones on their chest, given that they escaped slaanesh before The Fall even happened? Or do they still suffer losing their souls to slaneesh after they die more to the point?
Exodites do need and use spirit stones, since Slaanesh craves for the souls of all Eldar (Dark Eldar simply try not to die, either by vampirising life energy from others' pain, or by being rebuilt by Haemonculi). The difference is that they don't have Infinity Circuits, but Worldspirits, which are hidden structures of Wraithbone where they put their dead's spirit stones =)
About dark eldar and eldar that die in webway i think that their souls and bodies are taken by loughing god and transformed into harlequins. Do you see that after battles which hapen in webvay includin eldar and dark eldar there is a harlequin increase
"A peculiarity that sets the Harlequins apart from their craftworld and Exodite kin is that they do not bear Spirit Stones. Normally, when an Eldar dies, their unprotected soul is devoured by Slaanesh unless it is preserved inside one of these mysterious gems and joined with an Exodite World Spirit or CraftworldInfinity Circuit. Yet the Harlequins alone possess a secret that allows them to escape Slaanesh's jaws, and it is not one they seem willing to share."
"The most startling truth of the Solitaires is that, unlike other Harlequins, who are protected by their faith in Cegorach, their souls are doomed to be devoured by Slaanesh, although the Laughing God attempts to intercede on the Solitaire's behalf after their death and force the Prince of Chaos to compete for his or her soul."
Aresius King, the info above lends some credence to his theory, if the soul/lifecycle of a Harlequin were this intimately involved with Cegorach, then it would fit nicely into lore, if the death and rebirth was regarding the Solitaires. Much like a god of Chaos might spawn beasties or warp creatures into their likeness, the Laughing God could be so involved with His Solitaires.
If every Eldar that died was transformed into a Harlequin, there would be a huge number of Harlequin Troups, instead of the few that there are (think space marine chapters vs all the rest of the imperium of mankind for scale), Harlequins would have a force that would rival the entirety of the Eldar. Harlequins that die, may be recycled by The Laughing God, but only Harlequins, and to some extent Solitaires of the Harlequins, are protected from Slaanesh without soul stones. If there is growth with Harlequins, lore could incorporate Eldar souls lost in the webway (and therefore protected from She Who Thirsts) as being recycled into Harlequins by Cegorach, Harlequin souls themselves, and a few Solitaire souls. He is the strongest of the Eldar Gods in my opinion, as he was the only one to survive the Fall of the Eldar Gods. It would make sense that he could create a devout spawn in His image, like the gods of Chaos do.
I'm with the last commenter - the other guy said ALL dead Eldar are reborn as Harlequins, which doesn't fit at all with the "dying race" story of the Eldar.
About the origin of the Solitaires, which are a special breed of Harlequins and not "daemons", why would a "cegorachi spawn" be doomed from birth to end up in the belly of another god? I think it has more to do with tainting their souls from playing the She-who-thirsts role in Masquerades.
I’ve heard a bit of a darker reason for a Solitair’s exisitence. I’m relatively sure it’s from old fluff, but very cool. One of the first trials an Eldar will been faced with in his becoming a Harliquinn is to expose his soul to Slaneesh and survive, without it being consumed. Many are, and once their soul is eaten by the Prince their body dies. The ones whom pass become the Players and Harliquin members. However, a very small minority of Eldar expose their souls; it is consumed by Slannesh, yet their body remains. It is these haunting figures, already dead basically, that play the role of Slaneesh in the Act’s of the Fall. Pretty fitting role I guess, since their soul is already eaten by her.