The reason the Red Wedding worked is because three fan fav characters (who no one could dislike) died. If that happened in a DA game everyone would just reload from their last save and play again (maybe taking characters they don't like to die instead), if there was a single save (no backtracking) feature then it would be very effective...
Maybe the final mission could result in character deaths, depending on how well you've prepared Skyhold or how positive your relationships are with characters. Maybe some followers (Solas, Sera, Cassandra, Viviene, Varric and Dorian) who seem to have a purpose in the story going forward would always survive, but some 'doomed cases' like Blackwall, Iron Bull or Cole could make dramatic sacrifices which are out of the player's control?
Imagine Iron Bull yelling Krem and the rest of the Chargers' names as he charges head on into an unwinable battle, this would only happen if they died in his personal quest, but he'd not sacrifice himself if they're alive (because he has something to live for...). Or something along these lines...
Side note, is it confirmed that Blackwall dies if you leave him in Val Royeaux? Since I've always saved him I don't know, there is nothing about it on the wiki (or atleast I didn't see anything). Maybe he's just stuck in his jail cell, maybe a prison riot between games could free him if he is to return?