Brin was the psicrystal made by Virikhad, and embodied the kalashtar's Faith and desire to do good. When he and Virikhad swapped bodies in the Bonetree Mound, Virikhad refused to murder Brin to reclaim his body and Brin was not powerful enough to fully self actualise and become a person.
Brin died when Virikhad's body did, and his consciousness was eviscerated when the mind flayers ate Virikhad's brain.