If you are astral projecting in the palace of whispers
(Palace of the lich queen of the Githyanki in the astral plane,
Tu'narath) and you are slain, would you awaken in your physical body back on the prime material plane, OR would your soul be trapped in the walls of the palace since it says, "Any one who is slain in the palace of the lich queen, their soul is trapped in the walls, and can only be freed by a wish, resurrection, etc..."
I'd say trapped.