See, I thought of it the opposite way
I already did the crazy train tragic romance that ends horribly with my Hawke and Anders. Killing her in the Fade only sealed the deal.
I'm ok with Solas's story being sad. But he is not dragging my Lavellan down with him. She's young, bright, resilient, and she actually WANTS to make Thedas a better place. Despite all the heartbreak of the Solas romance, I'd say she came out of her game much stronger and less jaded than my other PCs. I am not losing my only truly heroic Dragon Age PC to tragedy.
EDIT: And if Solas dies and Lavellan survives, I already have a bittersweet headcanon in place. I may have thought too much about this right after finishing DA:I 
My Lavellan might consider helping him if the option is there, the reasoning/methods are valid, and certain truths emerge, but if things end sadly, she'll manage to go on somehow, with her friends and responsibilities, and the life she has managed to forge. All of her experiences are worth something.
My biggest worry is that they're going to make him do something really OOC, like "SCREW THIS WORLD IMMA RELEASE ALL THE GODS EVEN THOUGH LOCKING THEM UP WAS PROBS A GOOD THING". Or "I KNOW WE JUST SPENT THE WHOLE GAME FIXING THE VEIL BUT I'M GONNA RIP IT AGAIN JUST CAUSE!!!!"
I highly doubt this will happen, given a few things. One, they spent so much time seeding his character in the first two games and also through DAI before the reveal. They made him a highly layered person who genuinely cares very deeply though he carries complex emotions from all of this. He's self-denying, regretful, and even a little bitter to some degree, but he also can't keep from caring about others, despite trying to keep them at arm's length.....even attempting to teach or help the Dalish in some way, the people who utterly revile him (in their misunderstanding).
What Weekes said about making sure that Solas doesn't lie much, and that he treats the Inquisitor, especially a romanced Lavellan, with respect and isn't coming off as using her, these are important. And not signs of someone going cheap OOC villain or anything.
While his dedication to his goals could see him forced into an antagonist position, with Weekes taking over as lead writer for the series and the love he clearly has for Solas, it might wind up sad, but it will, IMO, remain true to character.