^ But, so long as we are bringing non-fiction into it, there are cases of people falling off of farther heights and surviving.
Couple the ambiguity of her "suicide" with the vague nature of her fate in the keep and, well, the door is open for BW to bring her back.
You appear to have a rather static picture of the world in your mind. I could mention several successful revolutions in real history that started by an "outcast" returning and shaking things up, and the people in power did not manage to contain them. Of course the magisterium isn't goint to like either of them. That is irrelevant. Such things haven't stopped people before, you know? No plot armor is needed, just a plausible setup.
As for religion, eventual co-existence of two sides of a schism isn't exactly unheard-of either.
For my part, I can definitely see him return to Tevinter. I fully expect it, even.
I just do not think he will be able to reclaim his status right away when he does get there.
And, more importantly, I think he needs to grow a pair. Dorian is a wuss, IMO.