Kyjal was the only survivor of the defeat of his master. He fell into the sea below Tir'in'tiral and was presumed dead. Once that part of Sildëyuir was cut off and became the Night Realm, Kyjal found his master's corpse and extracted his brain. He placed the brain in a jar of embalming fluid and then the jar into a chest cavity he had made in a Girallon. Then, using a technique Mourel had been working on, Kyjal animated the brain. Kyjal helped his master animate all of the corpses in the Night Realm and aided with Mourel's experiments for the rest of his life before trying to make himself a lich so he could serve Mourel forever.
The process succeeded in killing him, but he didn't come back as a lich. Instead, he became a Deathlock with absolutely no memory of his past. Carving a hole in his head, he placed the remains of his spellbook, a partially shattered King's Tear inside so that he could still cast spells, but spent most of his time in a maceration vat.
Kyjal was finally killed by adventurers while they battled through the Night Realm on a quest.