I think most people say they'd kill their Hawke online but won't do it in the game unless they're doing a completely evil playthrough. Ultimately, it's someone they played with for a full game and like or dislike, someone they embodied for a bit. Now granted, I hated DA2 (still play it a little here and there but mostly now for Hawke's appearance). As much as I hated the game and what they did to a few characters I don't think I will kill Hawke in all of my playthroughs. Because as much as I hate that game and what it means about BioWare's "evolution" (along with ME3 which I hated more [oddly enough]) I still don't think I can kill someone who's a part of me every playthrough. Because that is ultimately what Hawke is and we all know this.
I think for as many people that say I'll kill Hawke on every playthrough I bet there will be a time when they leave him alive just for laughs. Just like those that chose Bhelen. And if not, they're not playing it for the story. They're metagaming for their own desires which is perfectly fine, but shows a truly extreme and judgmental mindset that I find revolting. After all, if you can't look to see other view points, than how can you truly respect and come to your own? All you see is what you think is right without challenge or flaws and without that your logic is nothing but flawed. And if that's all you are then what do your opinions or choices to the rest of the world state? That you're a person that no one should truly listen and take council to except when the broken clock is right twice a day.
So yeah, I'll keep him alive on a few playthroughs and I'll kill him on a few others. My canon one will keep him alive. My canon will also (if reports are true) keep Varric alive and not demon possessed. However, I may also leave Varric to die in a few playthroughs with the lyrium idol or have him be possessed. So... we'll see. After all, the Inquisitor doesn't know Varric like Hawke does and if it were Hawke in the same situation: I don't see him/her killing Varric. S/He may leave him or try to save him, but I don't ever see Hawke killing a possessed Varric. I do however see the Inquisitor doing so and I can live with that, but it's hard for me outside of story. Not in it.