Advanced technology in planetary core observation centers that stretched thousands of miles into the planet were ejected within pockets of liquid metal when Eterna - The Heartworld was destroyed. The chunks cooled upon exposure to space, trapping generations inside.
Some groups of Fehralin survived in these enclosures. When the Gods agreed to The Cycle and created The Sheltered Plane, many of these large chunks of rock were captured within the atmosphere. When the Fehralin made their way outside the facilities after generations, they found themselves in a breathable atmosphere.
One of the larger facilities that contained a sizable population broke free of their containment, and found themselves floating on a chunk of rock looking down at a broken planet. Broken, but alive. Through some clever engineering, they were able to perform a controlled crash, slamming the chunk of rock into the planet. The resulting crater in Eterna resulted in the founding of Üd'Breah, capital of the Fehralin civilization.
The Fehralin struggled to survive, many losing their lives in the early generations. However, through their struggles a civilization was born. The Fehralin, constantly exposed to the purple light of Agavina, The Dark Star of Eterna, evolved into modern Dark Elves. Their understanding of technology was lost, but their magical capabilities grew, and resulted in a thriving civilization.