Brakkal is in a cage in the goblin camp. I decided to kill all the Absolute worshipping goblins so he would feel better. Brought him the dead goblins like a cat would. I left him in his cage though, because he worships Maglubiyet and he is probably evil. Right? ;)
You can also shoot the chain. Or just open the door to the cage and see what happens.
Honestly, now I kinda wish there was an option to convert him via one of the divine casters.
Bring him in as a camp follower, at minimum, during a evil campaign.