Just to add my two cents on Solas' future plans and what they mean for Thedas......I believe that he is speaking quite literally when he says "Doing so will most likely destroy your world."
Why?
Because his original plan was to lower the Veil from inside the Fade, probably because he guesses that is the best way for him to survive the rejoining of the two worlds. And he doesn't have to be in the Fade to lower it from what we see in the game. You have the Breach and whatnot so it must be possible to take away the Veil from either side. Not to mention the fact that clearly Solas constructed to Veil from the physical world, so in theory it can be deconstructed from there as well.
The only logical thought for me then is that Solas does expect full on burning chaos reigning down on Thedas and odds of survival are better if you are on the Fade side.
I also completely draw the line if Solas ends up sacraficing tons of modern elves to walk the Fade because at that point he truly is as bad as he claims the Evanuris to be.
It doesn't really mean that for certain.
What if the Veil can be brought down from the Fade in a safe manner, but the unchanging nature of the waking world wouldn't allow its' safe removal?
What if bringing the Veil down from the unchanging side of the Veil will cause spirits to be sucked out of the Fade?
We can't really know why it is important to remove the Veil from the Fade, Solas is the one who put it up, he is the expert. He put the Veil in Skyhold, in the unchanging world, maybe he needs to do the opposite to remove it, otherwise you'd end up with a massive breach instead.
There is also the issue that there are many ancient elves roaming about modern Thedas, if bringing down the Veil from the Fade was to only way to stay alive then the ancient elves would've died as well.
Anyhow, the dialogue with low-approval Inky seems to hint that Inky would survive the Veil dropping and that's why Solas can't tell them why the current world has to die, so he won't give them tools to use against him.