In my opinion, Solas has no idea of what he is doing and he will screw up big time as always.
If we account for the revelations of Descent and how the Fade looks like in it's raw state (full of lyrium veins), we can make the fair assumption that the place it's made and held together by the dreams of the Titans who themselves are immortal and godlike entities by nature.
Elves weren't originally immortal in any sense, the Evanuris won a war, against whom we speculate to be the dwarves, thus obtaining control of the Titans and their blood which was used to master the Fade and in turn reshape reality to be how they wanted.
Oghren in Origins credits the agelessness of the Guardian to the massive lyrium deposits in the mountain the Temple of Sacred Ashes was build in and that guy alone had enough power to keep a small army of Reavers and a High Dragon at bay.
If we are to believe that lyrium and the Titans are the source of the Evanuris godhood and that the Evanuris, by controlling the dreams of the Titans and channeling their power to their servants, were the source of the elves magic and immortality then you can be sure that Solas is going to shoot himself in the foot.
Back at the days of Arlathan before the Veil, there were no humans in Thedas and much less mages amongst them who knew what they were doing. If Solas tears down the Veil that will open the possibility for powerful and corrupt magisters to seek control of the Titans and obtain the same sort of power the Evanuris had which will be ten times worse for the elves or anyone else for the matter.
Solas pretty much underestimates everyone who came after the ancient elves while forgetting that their own might came from pillaging the gods of nature that came before them.
The bad future all but shows that Corypheus, who was a human to begin with, managed to conquer the world by corrupting the Titans with the Taint and using red lyrium to enslave every race to his thrall.
If he had managed to obtain the Anchor as he originally planned, he would have entered the Black City and probably obtained the same kind of power to reshape reality as the Evanuris had which would have been ten times worse.
Speculations apart, the point is that elves aren't any more special than humans, they just tapped into the power of the real gods first and abused that power until it destroyed them.
Solas, being the idiot he is, thinks that destroying the Veil now even if it kills most humans, kossith and magically inept elves will pave the way for the true Elvhen to return to glory but in reality all that accomplishes is to open the path for the most powerful mages of any given race to race after the Black City and control of the Titans just as the Evanuris did before them.
All that potential problems without even accounting for what the Taint and Blood magic, completely different kinds of magic than those related to lyrium and the Titans, might do to the world once they have unrestricted access to the Fade and the Titans themselves.