I'm guessing the next invasion will not happen. At least for a few more Ages, if ever.
I'm thinking that there will be a great upheaval in Seheron if not a little farther north. The Qunari can't be the only people in the north, and perhaps there would be an organized rebellion. Probably even a schism within the Qun. What madness that would be, right? Perhaps a non-qunari Qunari finds a slight flaw or develops the philosophy further which is rejected by the more traditional qunari Qunari but accepted more by other Qunari, causing conflict. Perhaps the idea of changing it slightly for easier conversion causes disagreement among the leaders of the Qun.
Perhaps a group of dissenters/doubters organizes and proposes a new philosophy, maybe even a new religion, getting the Tal-Vashoth to join them (or a good number of them at least).
This conflict may weaken the great Qunari Empire, which would allow the Thedosians to invade north, maybe even open up trade with the north.