I'll have to admit I have this morbid curiosity to see how Cullen would react if the Inquisitor had actually died in the final battle.
It will break him I think... I can imagine a scene with a funeral service (funeral pyre for human, burial for elves) with everyone saying something for the quizzy, Leliana sang In Uthenara. And Cullen just stay at the back, in silence, can't say anything. When everyone had gone, he's still there looking at the ember, then slowly put the Coin to the pyre. And then his knees gave up and he let out a single sob and let a single tear flow...
But ok, I have to admit that I'm very interested in seeing that in game... Half the waiting (before spoiler comes out) I nearly expected that Cullen won't make it to the end or will die at the end/go mad or something like that. We did get similar option with Alistair (drunk/killed/good ending).
If we're talking about romancing villains... I 100% seriously serious no jokes have at least one Warden I ship with Loghain, and one Hawke I ship with Meredith. 
Bad guys are fascinating when they're well developed characters with depth and substance and character of their own, and more than mustache-twirling mwahahaha ~I am evil incarnate~ baddie bads like Coryfish. Killing Cory was like, eh whatever, you bad guy me good guy, time to die now - but I can rarely bring myself to simply kill off Loghain like that, and if there was any way I could have salvaged anything of Meredith, I would have.
Come to think of it... that's probably why I like Calpernia better than Samson as villains. Because you can salvage something of Calpernia, but you can only condemn Samson, with no option to show mercy or sympathy, or anything beyond blind hate. The game never gives you the option to even say something like, what you did was absolutely atrocious and I can't absolve you of that, but know that I understand why you did it. How I wished I could have said at least that much to him before going all, off with his head!!!
I wouldn't ship any of my Quizzies with Samson, though.
probably
Loghain is a hellishly well developed villain. The more I talk to Solas (he described Loghain once), the more I read The Stolen Throne & think about it, Loghain did what he did not just because of a lousy "I want to be God/King/whatever". His motive & situation just put him in a very gray area, for me at least.
That's what made DA:O a really good game, when the Big Bad Villain is actually in gray area.
This! It breaks my heart to think of Fenris being alone again after all these years. Imagine his face when he gets that letter from Varric. I can't handle that.
... I did that. And now I think that I'll have Fenris tracking my inquisitor like hell...