We're talking about a mandatory death of a Player Character here, so I think people are going to be pissed no matter what. 
Oh I don't know, some people get kinda romantic about their characters dying, haha.
In this scenario, Solas kills you at the end of this scene no matter what, but your actions determine how. Do you ask him to do it? Does he announce what he's going to do or do you work it out for yourself? Does he twist the blade in your gut or does he move in such a way as you don't even feel the Murder Knife until it's already over?
And most importantly: what do you pick for your last words? Do you curse him with your dying breath? Call him a monster out of time, just like Corytheus? Beg him to forgive the world for not being the way he remembers? Tell him you love him? That you believe he can be redeemed?
Player Characters always see their missions through. But your game is over. Would you still promise him that he will be stopped if you KNEW you wouldn't be there to see it?
OK. See I just can't accept that he would kill you if you didn't ask him to and he didn't outright hate you. I honestly can't come up with a scenario in which he would do that unless the suffering was extreme and he really couldn't take seeing it anymore. So let's assume that's what happens.
My quizzy is a romanced Lavellan, how would this play out for her?
He offers to help end it quickly. My Inquisitor would say no. She'd try to keep him talking up till the end. And she'd probably do her best to maintain eye contact.
So, the mark's getting bigger, pain is escalating, she's still talking to him. What would she say? She'd remind him that all the sentient beings of the living world aren't worth less than his need to assuage his guilt. And that as long as she's known him, he's been a person who respects people, who are beings of spirit as well as flesh. Even if he thought differently once, he can't kid himself now. And all his talk about granting merciful deaths means nothing if he is still willing to overlook the fact that he is destroying *people*. His ideals mean nothing if he's willing to throw away that many living souls for them.
When she sees that she may only have a few moments left, she'd tell him only two things: that she loves him. And that she hopes he finds another way. Really the two most honest thing she can say at that point.
Maybe, with her last breath, she'd try to kill him. She'd fail, of course, but she'd try. If that adds to his trove of memories with which to torment himself, fine.
What it comes down to is that as much as she doesn't want to cause Solas pain for his own sake, she's going to do everything she can for the world right up until the moment she dies.
(Man, I'm super impressed with my Quizzy right now
)