The whole lyrium thing is massively frustrating - for me anyway it was a huge retcon. I am also really curious to see where it goes in the future, given the closure of Trespasser.
(just coming back to this post after dinner!)
That's an excellent question for dwarf fandom, actually. Regardless of which ending you get, the Templar Order is severely damaged even in the best case scenario where you get to save and redeem them, and with many among the Templars remaining now looking into quitting lyrium if they can, the lyrium market is taking a serious blow. If you destroy them, then, the business is half dead in one single blow. And no, Tevinter Templars don't use lyrium or have any real magic-disrupting abilities (which brings up my usual question of how to preserve the Southern Templars' abilities without the lyrium to draw from), so they wouldn't count much either way.
Mages still do need lyrium, so the market is not entirely dead. Vivienne does say it has effects on them too, but apparently it's different from Templars because of their connection with the Fade, and some parts of Origins and Last Flight imply the lyrium is not something they can really do without... unless we trade lyrium for blood as magic fuel, and that's not where we wanna go, I hope. But still, you're right, at least half of the old market is going away and that's not good for dwarves. Orzammar's economy is already crippled and depends too much on the lyrium trade as it is, half of that trade going under (not even counting the business lost to the Carta black market) doesn't bode well for them.
I'm not sure I want lyrium entirely phased out of the story, though, because it's such a fascinating narrative element. I do want to see it elaborated on a lot more before that happens, anyway. Not many fantasy worlds bother explaining where "mana" comes from, it's usually just something that exists to facilitate magic and nothing more - the fact that the same mana source that facilitates magic and pseudo-magical abilities in this universe is also something that destroys the user in the long term is very interesting.
Even beyond its magical properties, lyrium is such a key element in dwarven economics and social structuring, and in surface underworld structuring too - we had an entire organized crime web specialized in enabling the Chantry-induced addiction of Templars, so where does that whole industry turn to now? But I think Descent is good sign for this subplot. Before DAI it did seem like they had no idea what they were doing with lyrium, like they were just winging it as they went and the story needed to turn this or that way, but now it seems like they've finally sat down and settled on the lore rulebook of what lyrium actually is, what it does, how it works, how and why it affects different people different ways, etc. We may not see all the rules clearly yet, but hopefully we have a consistent lore basis behind what we learn about lyrium now.