Reznik is a member of the Asylum Orderlies and he works at the Dixmor Hospital for the Criminally Insane. He can be seen behind a gate with Dr. Pickman and Mendez. If Dr. Pickman spots Daniel, he will order Reznik to escort him back to his cell. Reznik tries to contact Reggie to open the gate, but will fail. Then Reznick tells Daniel to wait there until he finds another way, but he will never really make it to where Daniel is, no manner how long the player wait. Thus, his fate is unknown, but it is most likely he was killed by another inmate.
Should be noted, Reznik will fail to open the gate even if Reggie was left alive.