I like to think Cullen, Barris and Rylen are the templar trinity of bros. In my head, they all get together once every few months (after inquisition) and have a boys night in (Cullen practices keeping his clothes for when he plays cards against Josie)
I didn't even think about Barris being dead if you side with the mages. I'm glad that templars are close to my inquisitor's heart 'cause that means he always gets to live
Although I miss not being able to meet felix, and telling Cullen that my inquisior wouldn't change anything because then she might not have met him. The price we pay for our character's canon 
This is canon. I'm absolutely certain that it's canon.
Also, it is canon that Barris never dies. EVER.
^ though, okay, on that note, did anyone else find that DAI sort of plays like 2 games in 1? 3, really. there's:
Plotline RPG - all the major quests
Skyrim RPG - wander around in a massive map and kill things
Sims - Haven/Skyhold time
and then there's the wartable, which was like an app game or something. push button, check in later and laugh at the terror that i let someone (usually cullen) unleash on thedas.
some of cullen's responses to wartable missions are epic badass. some of them are hilariously bad ideas. like, you just made SUCH a mess of that, but i'm laughing too hard to want to go back and make it right (<< mainly thinking his approach to the trevelyan family quest)