I don't expect it to be only positive, no. When yanking the carpet out from under something, there is a possibility of damage. But, if you pull the carpet out slowly then the object remains safe. With the old system removed, a stronger one can take its place. The transition is hard, but if supported properly and handled carefully it will stand.
For Tevinter specifically, they don't have order since the only times they get along well is when the slaves revolt. They have government and structure, but the negatives like slaves and blood magic are not needed for that. Just look at every other nation in Thedas. And finally for trade, there is more to trade than people. Find a substitute source, there is plenty, and it is no longer needed. The only reason they haven't I suspect is because they haven't looked, kind of a "If it isn't broken, don't fix it." mentality.
It sounds like you are talking more about reform than completely dissolving the Imperium. If that's the case, I agree, reform would be a good thing.
Change, though, usually has to come from within. If the Inquisitor or some other protagonist tried to impose it upon Tevinter, I could see that ending in a mess.
It's frustrating that most of our knowledge of Tevinter is filtered through the lense of the Chantry. Every nation in Thedas has it's problems (racism, religious intolerance, bigotry, internecine conflicts, politicking, underground slavery). I don't think Tevinter is really as bad as Brother Gentivi and others make out. Dorian, at any rate, seems to think that the imperium is worth reforming and preserving, rather than dissolving.