Okay, so I get that the chantry has to go – it’s what the entire plot of Inquisition hinges on, they can’t let Hawke prevent that. But I think what made a lot of people angry was not that you couldn’t stop it, but that you never even get the chance to try. That Anders behaves exactly the same regardless of your approval rating with him, regardless of whether you were romancing him, which speaks pretty poorly to the importance of that relationship.
So I propose…
If your approval rating is high enough (and this hinges on the friendship meter, not the romance meter, because he has to believe that you would side with the mages), he comes to you before he makes his move and confides his plans to you. You can be like, “Fuck yeah, let’s blow this thing sky-high!” in which case he’ll ask you to create a diversion for Orsino and Meredith while he plants the bombs, and off you go. The chantry goes up in flames.
Or, more rationally, you can be like, “Anders, nooooo!” and try to talk him out of it. You’ll get a choice of several different arguments (“This isn’t going to help” or “Too many innocents will die” or “This would make you as bad as they are” etc), but it’s tricky going, and if you don’t use the right one(s), he won’t be budged. It’ll come down to Hawke going, “I can’t let you do this,” and Anders going, “I can’t let you stop me.” And you will have to fight Anders. To the death. You will have to kill Anders.
Bear with me.
Alternately, you DO make the right arguments: Anders starts to waver. You’re on the verge of convincing him that there has to be a better way – when Justice takes over. Justice is too angry, too hell-bent on revenge to let these plans get derailed now, so he grabs the wheel, shoves Anders screaming into the backseat, and does his level best to kill you.
The Anders/Justice fight is HARD. It’s like the Ser Cauthrien fight in DA:O, where it’s possible to win, but you’re supposed to lose it. You’re losing, it’s come down to the final blow – and Anders pulls his punch, because he loves you too much to do anything else. I think that’s one of the most compelling aspects of Anders’ characterization in DA2: that he is in love with Hawke regardless of whether you reciprocate or not, regardless of who you romance. He just loves you. Which is why he can’t bring himself to kill you, and if you’re fighting Justice, then at the crucial moment when Justice is about to deliver the killing blow, Anders wrestles control back just long enough to weaken it. You tumble to the ground, your vision going black, and Anders whispers helplessly, “I’m sorry,” just before he turns to flee, or before his eyes flicker blue and Justice takes over again.
When you wake up, you make straight for the chantry, trying to intercept him, trying to warn somebody, but it’s too late – you get there just in time to see it go up in flames before your eyes.
If you WIN that fight: Anders dies in your arms. If you were fighting Justice before, then Justice fucks off as soon as you deliver the killing blow, leaving you to deal with a dazed, dying Anders. Dialogue here would be adjusted to reflect whether you’d talked him out of it/whether you were romancing him, but regardless, I expect it to be goddamn heartbreaking. He dies, and Hawke just sits there with his body until Varric or somebody comes along and is like, “Come on, Hawke, come away, I’ll take care of it, you don’t have to stay for this.”
Hawke and Varric walk out of the frame, footsteps fading, but the camera stays on Anders’ body. For a long moment it’s motionless, too still for anything living, and then there’s a twitch. A crackle of blue. And Justice opens his eyes.
Because we know that Justice can possess corpses. This has been in his job description since day one. The camera pans over his face and it is chillingly blank, and we know, in a heartbeat, that Anders is gone, that the corpse now struggling to stand is exactly that: his corpse. It has the same grotesque, visceral sense of wrongness as the moment when it was revealed what happened to Leandra.
Justice is the abomination that everyone’s been telling you he was from the start, no different from the dozens, hundreds you’ve dispatched before. There is nothing left of the well-meaning spirit that he was in Awakening, and nothing left of Anders either. The whole time, the boundary between Anders and Justice has been blurry, unclear where one ended and the other began, but with Anders gone we can finally see exactly what Justice is, what’s been inside Anders this whole time: a monster.
Justice gets to his feet, and staggers offstage to finish the job that Anders began.
The chantry goes up in flames.