A dark future vs. a path not taken: it's all time travel!

So a bit of context for my answers. First I have to recap the traditional interpretation of time-travel, then I can talk about how my interpretation differs.

In the traditional interpretation, you start in Timeline A. If you don't do anything, it goes off into a dark future. But, after traveling to that future, you are now armed with this knowledge and you go "back" in Timeline A and change things, so that that dark future doesn't happen. You "undo" that branch and head down a different branch. You change the future.

That interpretation is problematic and full of paradoxes, like the Grandfather Paradox (en.wikipedia.org/wiki/Grandfather_paradox). It's inelegant and offends my sense of an orderly universe.

Instead, I prefer the many-worlds or multiverse hypothesis. When a story depicts the POV character returning to their original time/place, I interpret that as the POV character travelling to a different timeline that looks similar to the first. In other words, I assume closed time-like loops are impossible, and if it looks like a closed time-like loop, I assume it's a new timeline with a similar state to the original. Furthermore, any time-travel, forwards or backwards, is inevitably to a new timeline.

For example, IHW starts in Timeline A, travels to the dark future of Timeline B, then travels to Timeline C that looks very similar to Timeline A only it's a few moments later.

Now that may all sound like a lot of mumbo-jumbo for no net gain in understanding over the traditional interpretation, since as far as your Inquisitor is concerned there is no difference between returning to a changed Timeline A or a new Timeline C.

But there is an important difference. In my interpretation, Timeline B still exists! Nothing was undone. That dark future co-exists with the brighter future of Timeline C and whatever happens with Timeline A. Timeline B still "exists" in the same way that any path not taken (like if you choose CotJ instead of IHW) still exists, considering all possible playthroughs.

QED, I consider any path not taken in the narrative as an alternative timeline. It behaves exactly the same way for all intents and purposes, so why not just treat it that way? It certainly makes it easier to talk about whether things like the events at Therinfall Redoubt are canon if you choose IHW. Of course they are, just as the events at Redcliffe Castle are canon if you choose CotJ. They are all just parallel timelines, and when you choose a branch in the narrative, you are choosing a new timeline.

With that understanding, here are my answers:

1. Yes it is canon, although it would need an asterisk, much in the way a dream sequence would (e.g, DAO Warden Taint-inspired dreams). It's not an experience a character would define as reality, but since it is something the player can experience in-game, I think it meets the minimum definition of canon.
2. No, I don't believe there is a significant difference. When all possible playthroughs are considered, it's just another timeline.
3. Yes, as a consequence of #2, like any branch in the narrative, the dark future one is just as legit as any other path not taken. Meaning there is a branch in the narrative where Leliana dies holding the line. Nothing is "undone", that timeline exists in some way.