I'm not married to the idea of it being exactly like a "Red Wedding" it was just the first thing that came to mind when I thought of a lot of big character death. I am, however, concerned about the possibility of the franchise continuing beyond five, if they do I think they'll have to wrap things up within this period of history. I think the further they push the current timeline, it'll get harder and harder to make previous choices come back in a meaningful way. Players will have to start filling more and more gaps in with head-canon, and continue to get frustrated when it doesn't line up. This will be especially true with a new PC each game, and a clear intention on cultivating a stable of returning characters, which is why I think DA:I was relatively bloodless.
What I think (and hope) is happening, is that their building to an apocalyptic "old vs. new" conflict. Morrigan's comments about "skeletal hands reaching from the past" gave me that thought. Since a lot of this won't take place until the next-gen (which will hopefully be a lot better than this one, Xbox One and PS4 are underwhelming so far, IMHO) I'm hoping they'll have the capability to bring back all remaining PC's, LI's, and surviving companions for a continent-spanning war that puts a meaningful cap on all the major plot threads that have been introduced in these first three (Morrigan/Flemeth, Solas, Chantry reform, Blights, etc.).
Bringing back old companions with new PCs would really start to get annoying i.e. Varric as a companion in DA:VII would really lose its impact. For me he didn't feel as close to my Inquisitor as he did to Hawke, and all my Inquisitor did was argue with the returning DA:O characters, as they are both of the "any means necessary" mindset that my Warden was (My Inquisitor was a bit of a softy). Don't get me wrong, I like that they didn't immediately (or ever) get along, but at a certain point I think an Alistair/Morrigan/Varric/Leliana could just tell a new PC: "Shut up, I've done this shite like six times now, I know what I'm doing, why the hell are you in charge?" and unless they keep giving PC's Chosen One status (which would get REALLY old) you really couldn't argue back. (my bad lost my train of thought and jumped on my "slow it down with new PC's" train)