If I were Solas I would gather elves who wants leave Thedas and liberate the elven slaves from the Imperium, then I would destroy all eluvians so the humans, and darkspawn will not follow, and get them all to another world to start over. I start by teaching them everything about elven history and the downfall of the ancient elves to teach the people to never again repeat history. Then I would set up a healing process by teaching elves meditation for healing themselves mentally & spirituality, then I would set up a system of unity among families, love one another, and build up structures of agriculture, libraries, schools, and houses. It would be a better alternative course than tearing down the Veil and the Evanuris would eventually kill Solas and chaos would rise again.
"Leave Thedas"?
As in going into a place like the crossraods? Or going to one of the "in-between" places that Morrigan speaks of?
Because even in theory it is likely that will not work given what we know from Trespasser/Morrigan. From what we can tell, most--if not all--of the things we find and see in the crossraods (save for what was brought there from Thedas itself) are like the books we find the Vir Dirthara. They are not really real.
They are ideas simply given form by our perceptions. You may be able to feel it, you may be able to smell it, you may even be able to taste it--but in the end it is just magical energies given form. We do not know if anything consumed from this landscape is actually capable of giving substance. This is significant because it may be able to determine if a general population can actually be able to sustain itself, by itself, without any contact to Thedas.
For instance, we know that when elves see 'trees' in the crossroads they have leaves on them. We also know humans see the same trees but with no leaves on them.
But say the elves perceive apples on the tree. The question is if one were to pick the apple off the tree and eat it, would that apple be 'real' enough to provide sustenance? Even though other races cannot see, hear, smell or touch it (and thereby putting doubt as to if it is real)?
Then there is the issue of dimension stability. We know that it is at least connected to Thedas in some way--otherwise the rise of the veil wouldn't have affected it so much. So trying to distance yourself from Thedas, despite the existence of the crossraods/in-between places already being tied to it, is not ideal. But we also know from our conversation with Morrigan that the crossraods are....not exactly as stable as they used be. If anything they seem to be in a state of slow, gradual decay. As with the rising of the veil, paths may eventually sunder, the ground may give way to nothingness, and buildings will slowly crumble. Do you want to live in a dimension that can one day not exist?
Imo, there are too many things that could go wrong with that plan. Unless we get distinct proof that the elves artificial dimensions can sustain real things on its own or leads to other natural (as in not created by the elves) dimensions that is independent from Thedas, trying to civilize anything like the in-between dimensions will only lead to disaster.