I think the reward is meant to be inside the tower, not anything from the gargoyle itself. Also there is the quest with the cursed woman after you kill the skeletons.
Perhaps this changed after the most recent patch, but on my initial playthrough at the end of the maze (heading up steps towards the tower) a gargoyle congratulated me and let me choose rewards.
I have looted all chests from the maze, and cleared the tower. I was wondering about rewards for completing the maze.
