Ok, so I don't have my fluff written out quiet yet. It needs a bit of work. Here's a few bullet points I've got written out, though.
Exodite world of Corella, in the Gothic Sector. Eldar tolerate IG and presence; IG maintains a listening post to watch out for Chaos ships that might've broken thru the Cadian Gate. Two major autarchs; one (male) known for charismatic leadership. The other (female) notorious for epic bad temper, studied with the Howling Banshees, Swooping Hawks, and Shining Spears.
Shortly before the Gothic War begins, the Eldar put up defensive perimeter in the asteroid belt outside Corella, slowing Abbadon's move to retake the Blackstone Fortresses long enough for the Imperium to prevent him from getting more than two. (Again, the Farseer told them to do it). Toward the end of the Gothic War, Abbadon test-fires both Blackstone Fortresses at Corella; the IG post is oblierated and the Eldar are forced to flee into the Webway to avoid extermination.
Normal webway route to Ulthwe blocked by nasty webway creatures. Corellan refugees end up in Commorragh, Farseer and all. Needless to say, they set off every alarm in the place. Farseer gets carried off by a Hellion gang; never seen or heard from again. Charismatic autarch cracks, cranky autarch beheads him and orders surviving refugees to more defensible ground. They end up moving into the (abandoned? lightly inhabited?) digs of a lesser Kabal very high in the towers of Comorragh- close to the Scourge roosts, but not close enough to attract their ire.
Time passes, and after about 500 years, refugees have integrated with Dark Eldar population as the Kabal of the Shattered World. Aspect Warriors slain (not that they had many to begin with) and their spirit stones kept by the former Cranky Autarch- now Archon. Guardians became Kabbalite Warriors, Storm Guardians became Wyches. Numbers augmented with clones thanks to local Haemonculi, deals made with other Wych cults. They train their own Reavers using debased Shining Spears methodologies.
Archon retains her Aspect Warriors' soulstones, the Farseer's runes, possibly a rock from now-destroyed Corella. Still cranky as ever- keeps her sentiment from becoming weakness, though. Her Trueborn (well, all of the surviving Corellans are because the Exodites don't have clone tank babies) still refer to her as "the Autarch," but don't allow lesser DEs to call her that. Her prior existence is an open secret, because if everybody knows then nobody can try to hold it over her (someone already tried; he's now a crystal chandelier).
Cabal image is a highly stylized pic of a Blackstone fortress blasting a world into pieces.