Well, before I make a suggestion, let me ask a question: What makes you so sure that Solas fully intends to kill the elves in his faction once his plans are completed? I get that he doesn't see modern elves as his own people, but is that really such an unexpected or horrible attitude? I guarantee you that if I was to meet one of my own ancestors from even a hundred years ago, they would not see me as one of them. I don't speak their language, barely know their customs, and I don't even have the same religious practice as they do. In that regard, I see Solas' view on modern day elves as not his own as fair.
I get that Solas must be stopped, that much is clear. But I think his desire to give the world back to the elves is genuine, even though he knows that a lot of them are going to get killed making it happen. My belief in this attitude is reinforced from what I've read in Tevinter Nights, which did feature Solas, and showed more into what he's doing in the North.
Anyway, back to the point at hand. I think, in the end, in order to save the elves from the repercussions of Solas' actions after he's defeated is to not dismantle the Dread Wolf's faction but to either install new leadership or take it over ourselves.
Whatever Solas may have done or is going to do, whatever his true plans are, he has done what no elf has in thousands of years: united both City and Dalish elves into a single powerful faction. One so strong that the most powerful nations and organizations cannot afford to ignore them, and have no choice but to take them seriously. That in itself is a huge victory for the elves. Even Briala didn't pull that off, because officially her own rebellion against Orlais didn't exist. Both Gaspard and Celene's factions were too arrogant to acknowledge elves as threat. The Imperium and the Qunari don't have that luxury.
Right now, in the North, the Qunari have invaded, and certain details in "Tevinter Nights" suggest that there could be some in fighting in the Qunari ranks. The Imperium is corrupt to the core, so in order for them to be able to push back the Qunari, there's probably going to be some serious house cleaning. Which is probably where our next PC comes in.
One scenario that I can see happening in the next game is, depending on our choices and actions, we defeat the Qunari and they have no choice but to go back to Par Vollen and lose all their gained territories. There's a major political and new social changes in the Imperium, which makes its ability to go forth and conquer untenable. Depending on what happens to the Imperium and Qunari, and the choices we make in Solas' defeat, we could end up set up the elves as the new major power in the North, and they take the Arlathan Forest as their new territory.
To me, that would be the most cathartic of outcomes. The Qunari see all baas magic and history as something to stamp out, and the Imperium takes national pride in enslaving elves. Then for there to be an elven state right in the middle of them, and is more powerful than either the Qunari or the Imperium, that would set the world on its ear. I think that would be an awesome way to end DA4.
That's something that always bothered me in DA:I. We rebuild the Chantry and save the Orlesian Empire, both of whom are notorious for their mistreatment and crimes against elves, yet we did virtually nothing for the elven people. That's why in the next game, despite what Solas may be doing, I hope we can actually do something for the elves that raises them as a people.