Wynne can die in DAO. She goes on (if not dead) to get into a canonical but extra-game situation with her son and his lover, who are mentioned in DA:I, Rhys and Evangeline. Cole talks about them (and the events of the book, "Asunder") and there are a couple of war table missions about them.

The thing is, in the book, Wynne sacrifices herself to save Evangeline (again, Cole specifically mentions this). So.... if Wynne dies in DAO, how did the events of "Asunder" happen? Why is Evangeline alive? I've thought about it for a while and it's a tricky one to piece together, given the specifics of the story and the way Wynne saves Evangeline, it's very, VERY difficult to come up with an alternative as to why Evangeline is still alive.

And they don't even try to. As far as BioWare are concerned, Wynne was alive at the end of DAO, regardless of your choices or your worldstate. Either that, or they didn't think about it very hard. Or they didn't pay attention to their own lore/canon (despite the fact that you can have Wynne dead in the Keep).