I don't know, I genuinely think Solas -might- be willing to put Thedas at stack to further whatever his plans are, especially if he needed that much power. (( From the Orb/from Flemyth.)) He's pretty much going all in or nothing.
I can't think of what he'd be interested in saving that would warrant sacrificing Thedas. He is not fond of the elven gods, he is not fond of the elvhen empire... so whatever changes he intends to pursue are probably not for either of those groups. What's left? He'd be re-installing a system he knew already failed and while Solas is the King of Messing Up, I don't think he's quite dumb enough to repeat mistakes verbatim.
Plus there is plenty of evidence that he is compassionate towards the people of Thedas: you get approval from helping refugees. He slams Dorian for not helping the slaves - of all races - and condemns the Iron Bull for putting the Qun ahead of his personal freedom/the Chargers. He laments the loss of dwarven culture almost as much as he laments the loss of his own. He ends up caring for almost everyone in your party to some extent, especially a romanced Lavellan. I can't see him saying "screw this" and blowing up the continent without taking some measure to protect at least the people he values. Because then who would be left...?
Now if bad-relationship Solas were the only one available, I could totally see him sacrificing lots of people for his goals. In those play-throughs the Inquisitor is a confirmation of everything he thinks is wrong with the world. I could see a "wipe the slate clean" mentality coming from that relationship. But it's so far removed from the other types of interactions you can have with him that I don't think they'd write a story where only that line of character development made sense.