Isn't Cassandra saying that the person we know now is to become the Inquisitor in this game 'walked out of the Fade' i.e. after what she just has called the Breach. Someone or something has breached the fade which is threatening to destroy everything.
I would guess (and that is a qualified guess based on what Cassandra says in the trailer) that what she means is this:
The only person surviving the Breach is you, the Inquisitor. The Breach has been made? to make a tear or breach in the Fade, so that the Fade actually covers the physical real world. The Fade lowers itself down on the real physical gulf, this swallowing up or engulfing anything in its way. And for some reason, the Breach, at the peace conference, lets you, the Inquisitor, still live - without any memories of your survived, though.
And yes, all these tropes/clichees have been used before; however it is not that Bioware uses these tropes/clichees - it is the way Bioware uses them. We still stories about dysfunctional families, or stories of father-son or mother-daugther bad or good relationsships. We still watch stories about crime and detectives solving puzzles and cases on tv - also stories which uses more tropes/clichees that Bioware does. It is in in the tale is told, or as the old folk would say, how the yarn is spun, that the master storyteller reveals herself. And Bioware spins very nice yarns, imo, they tell very good tales, I find.