What If Solas Succeeds?

In the universe of Dragaon Age, the Veil that separates the Fade from the rest of the world is not a physical thing, despite references to it being torn and breached. It's more a barrier, like that mages cast in battle, to be dispelled. Even its name implies a thin covering that hides rather than a solid wall.

Consider the codex entry on the Veil which can be found in all three games, giving it more heft as “the devs see the Veil this way and want the player to know it” than the mere conjectural nature of half-blind research would normally carry.
"Regardless, the act of passing through the Veil is much more about changing one's perceptions than a physical transition. The Veil is an idea, it is the act of transition itself, and it is only the fact that both living beings and spirits find the transition difficult that gives the Veil any credence as a physical barrier at all.”

It's a spell that Solas cast, expending vast amounts of power (as well it should require, considering the magnitude of its effects). We don't know the source of that power, whether it was inherent or drawn from people or amplified by his focus or all three. We do know that it had the effect of making everyone half-tranquil compared to the way the world used to be.