Ah reading through this thread is a good lark, one simple truth remains. when it comes down to it war stories are morality tales.
so we have
Tevinter: a nation that once ruled all of thedas despotically, but since its reformation has made no aggressive moves against any nation in thedas despite this hysterical belief that they want to take over again and of course slavery.
Qunari: basically a NAZI religion, discrimination against groups (Saarabas), eugenics programs, spread the ideology through warfare, superior tech, forced indoctrination, labour camps and overt sense of superiority.
Now we've already seen on a small scale attempts by the dev team attempts to redeem tevinter, presenting it in the form of the Dorian project. a good guy, Who wants to fix whats wrong with tevinter. So you remove slavery and what is really wrong with tevinter? can't be the magiocrisy(sp) because thedas all countries are feudal house's kings lords etc, and all of those ban mage's from ruling. there's no moral argument from there. claims that tevinter will try and take over are unfounded, there's no reason to suggest it tevinter has never been the aggressor in a war since the Glory age.
So if the reforms with slaves goes ahead what would a war been Tevinter and par volley look like?
on one hand the only nation completely open to mages who hasn't been a aggressor in centuries thats been valiantly defending its lands from invading forces since its foundation, stood against blights, revolts marches, invasions since its founding. and has fought the Qunari threat for 200 years.
on the other? a nation of Horned NAZI's, who if they won would slaughter every mage in Tevinter. It's literally TAKE OVER THE WORLD vs the country that has stood as protectors of the realm for years conflict.
Given as every story needs a good (or less bad) guy and the US's whole deal with slavery, even in a fictional setting a country with slaves cannot be supported so the task is reshaping war mongering eugenics loving qunari we can easily see that Slavery will be abolished in Tevinter before this war is won. (in fact that's how they can win it freeing all slaves and getting them to fight with them against a common enemy)
I understand this forum has a strange love for qunari, mainly because they are alien i'd assume. But the fact is morally their pretty scummy people. you cannot have a group overtones of NAZIism win a war, you think the end of ME3 sparked outrage? this ending would be all over 24hr news channels.
I mean not only are these guys NAZI's but like the real NAZI's their seems no end to their evil war mongering way's, If Tevinter was to fall to the Qun the next country simply becomes the target.
Morally the Qunari cannot win such a war the bad guys winning? that would be like an option to have the archdemon win it lacks sense. But what about the people who love the Qunari? well sadly as we've seen earlier its a ton easier to redeem tevinter then it is the Qun. Fixing the Qun to make it palatable to most people would require so many changes that it wouldn't resemble the Qun at all. so the Answer becomes? make the Qunari more evil, frankly i'm not sure how they can be more evil then they already are without turning them into cartoon villains maybe have them make coats out of Mabari puppies? or have them kidnap people and have them kill defenceless children oh wait? oh i know Murder the just ruler of a city….. hmmm nope unless they become a pack of rapists dead puppies looks the go.