My feeling is that for achieving his goal, Solas will have to do something really terrible, maybe even destroy the world to start anew.
When Cole says in his banter: “You’re real and that means everyone could be real. It changes everything, but it can’t…” It means that whatever he is planning is no good news for the people of Thedas. Or maybe he'll even try to go back in time (like in Redcliff) to prevent himself from betraying the gods (explaining why he needs a lot of power) and change the future.
I guess we'll see, but if it means destroying the world and betraying your friends and family, I can't see my Lavellan doing that. She might tell Solas she understands what he's trying to accomplish and why, that she still love and respect him, but she have to stop him.
I'm not even sure Solas would actually respect someone who betray their friends and duty for a selfish reason such as being with the person you love. If you choose to go with him because you deeply believe in his cause, then it would be fine. He seems to respect people who can stand on their own, so dropping everything for a man, I'm not sure how he would react...
So maybe Lavellan can talk him out, fight and spare him, or help him find another solution (she's definitely wiser, more patient than him in my opinion and maybe come up with a better solution, or a compromise). Or maybe It's nothing as bad as I think and she will gladly help him achieve his goal 
EDIT: And I have the feeling that he'll contact Lavellan from the Fade at one point. I mean, he's the Dread Wolf, so I'm pretty sure he can't be found unless he wants to. And if he wants to talk to Lavellan, or ask for help, he won't risk approaching Skyhold. He might trust Lavellan, but not the Inquisition.
So I'm pretty sure we'll get more Fade time with Solas. And they'll be alone. That makes it better.