I'm certainly going to try to stop Solas in the future, but it might not necessarily have to end with his death. A lot of people seem to have kneejerk reactions to a character doing something that they don't like/don't approve of without bothering to look beyond the surface, and then they're all "LET'S KILL <INSERT NAME> BECAUSE HE/SHE WRONGED ME OR SAID/DID SOMETHING I DON'T LIKE!!!!!!"
Look, from talking to Solas and actually listening to him, it sounds like destroying Thedas is something that he doesn't particularly want to do but is resolved to do in order to repair the damage that he originally caused. I went into this stuff in a lot more detail in that other thread about Solas allegedly being the same as Corypheus (I said they weren't even remotely the same), but basically, it's my opinion that it might yet be possible to reason with Solas and that he maybe even kind of wants you to prove him wrong yet again.
Though he is certainly intent on undoing what he views as his mistake (no matter what it might cost), who knows what the future might hold. One would hope that there's another way to go about stopping him besides just killing him. As my Inquisitor said, she's going to try to save/redeem her friend IF possible. I don't want to kill him, but if I have to, well, I'll do it.
And as I will point out like I did in the other thread, if Solas were a complete monster a la Corypheus, he wouldn't have saved you (yet again) and allowed you to leave unharmed. Let's face it, leaving you alive is pretty much inviting you to come back to stop him, even if your Inquisitor can't necessarily go adventuring like he/she used to. Though now that I think about it, who's to say that a combination of clever dwarven engineering and magic couldn't result in a functioning prosthetic arm.