The craftworld Lia Fáil, lost since the Fall, was indeed not derelict. As Nuada's corsairs cautiously explored the dark, dusty worldship they were met and challenged not by squatters of the lesser races, nor even living Eldar, but the ghosts of the craftworld itself.
Active squads of wraithguard and wraithlords converged upon Nuada's host, ready to repel uninvited boarders. These dead sentinels were ancient things, the colors of their wraithbone bodies muted by time and dust, worn from ages of simple entropy. Deceased or no, Nuada was loath to wage war against his own race, and quickly ordered his followers to surrender.
The Doom of Lia Fáil
The newcomers later learned that the craftworld had suffered greatly after the Fall. The great ship was too near the Eye of Terror to escape unscathed. Many of the ship's inhabitants perished, and others were turned, corrupted by the apotheosis of Slaanesh.A battle for survival followed, and the eldar of Lia Fáil purged their craft spire by spire and deck by deck. In the end they were able to destroy or pursue into the Webway the last of the daemonic incursion, but sealed their webway portals as a safeguard. Believing themselves to be the very last of their race, they began a long, slow guardianship of the craftworld, and the Lia Fáil dwindled and perished over time.
Even the long-lived eldar are not immortal. As the surviving eldar succumbed to despair or age, the last of the craftworld's spiritseers bound them into the infinity circuit of the great ship, activating some to keep watch as wraith units. Eventually even the last of the seers perished. Without the guidance of spiritseers, or bonesingers to repair them or craft new bodies, the wraith constructs held silent and eternal vigil as the great craftworld silently slid through the endless darkness between stars, a tomb to a forgotten people. These last protectors, neither living nor dead, call themselves the Forlorn Host.
Lia Fáil Rises
Nuada, through his son Daghda, bartered first a truce and then an alliance with the spirits of the infinity circuit and the long-sleeping dome of crystal seers. Bringing his displaced people to inhabit the empty craftworld and return it to life once more.
During this period of reconstruction, Nuada names himself High Autarch; a title hearkening back to the most ancient myths of the eldar race. Bringing together the lost Nemedian exodites, he opens trade with Ulthwe and Altansar (the latter costing him some good grace from the more suspicious eldar tribes), Yme Loc and Ybraesil. The ranks of the new Lia Fáil craftworld fill; its streets bustle with activity, its parks ring with music and the gentle laughter of the living once again.
But Nuada is devoted to the craft of war. And Nemed is not forgotten...