I had no issue sacrificing my Warden, despite how much it would obviously have hurt Alistair (although the game never did that scenario any justice) because... let's say I was on a very different wavelength the first time I played Origins, and my Cousland took a few weird turns over the course of the game that made her a rather ugly person towards the end, so her sacrifice at the end of all things was something of a catharsis. She had to die. She may have needed a fairy tale happy ending, but it wasn't the one she deserved.
Unfortunately, Alistair, Anora and Loghain were all casualties of her journey, and in the process of burning herself out she ended up taking them all down with her. It was an ugly mess, but it was my first playthrough, and often times that's the one that sticks, isn't it? Even after replaying the same character and making different choices and giving her different endings, that mess of a first playthrough is the only one I feel is her genuine, legitimate story. I guess that's detached me from the need to give Alistair a truly happy ending, despite how much desperately deserves one, because it doesn't feel real for me. It's cute, but it's "alternate reality," it's all those alternate characters and playthroughs that you don't take as seriously as your main one. That's why I feel icky about retconning her death, even if a sacrificed Warden was worth nothing in Inquisition after all, and a living Warden still has some minimal hint of continuity. It wouldn't feel right.
My Hawke is completely different question, though. Different times, different story, different wavelengths... I need her to be happy. Hawke suffered too much, she lost too much, she was hurt too much for nothing that was ever really her fault... I don't know if I could say I feel closer to one or another character because they're both my darlings for different reasons, but while my Warden's life means nothing for me, my Hawke's happiness means everything. Even if her love interest is not a particularly tragic figure, and is mostly the guy I chose to make her happy (as opposed to how I made my Inquisitor to make Cullen happy), I couldn't bring myself to split her and Sebastian because that'd be one more thing she loves and loses, and I can't handle that. (lol, how melodramatic
) And I definitely could never sacrifice her life over... pretty much anyone but maybe Bethany. And I'd still cry for years if I had to do that.
SO, what I mean is, to me it's on a case by case basis. I don't think I could sacrifice my Hawke and my Trevelyan because there are circumstances to their survival that I'm not willing to give up.... but my Cousland is easily a goner, and should probably stay that way. 