I like this idea that the Geezer is a prisoner in his own fortress, and someone else is using his power. The poison gas is a nice angle that does a good job of pitting expedience against morality, and morality against chaos, so that the low chaos route isn’t automatically the right thing to do. (This is not to say that sacrificing all these mooks so the selfish crime boss can get his wish is the right thing to do. I’m just saying this isn’t an obviously clear-cut choice.
Then again: Looking at it from an in-character perspective, if I was Daud I’d think there had to be a way to disable the poison gas bomb so that it would be safe to kill the geezer without dooming everyone else to die. Somewhere in the system there’s a trigger that will release poison gas if the geezer dies. If I was Daud I’d want to see if I could find that trigger. Or find a way to spoof the system into thinking geezer was still alive. Or trigger an evacuation. Or expose Trimble’s scheme to the Geezer’s men.
Maybe some of these possibilities are addressed in the game. Like I said, I haven’t played this, but these are the first things that came to mind when watching Josh play.