I actually did this on accident on my tactician dark urge playthrough. I broke into the fortress through the prison and fought against all the guards, then Gortash got randomly triggered aswell as some other guards. However no steel watchers were alarmed, the other guards and Gortash needed 5 turns to run down the stairs and get to me, but by then the rest of the guards were already dead and I had an easy fight against him. So far I dont know what happens afterwards but if you do it like me you can definitely beat it on tactician, even tho its not the intended way. I also had zero dialogue with Gortash, he just ran into combat and died, kinda sad. But the whole fight took me around 1,5h and was ultra laggy so I wont reload after sitting through all that.
