I don't think we will see the end of the Ascians in 3.xx. Assuming we are going North (Ishgard) and North West (Sharlayan) we still have the Ala Mhigo front to explore, the Ascians are very deeply tied to the Eorzean land, so if we don't end up traversing the North East I don't think we will kill all the Ascians. That being said I bet we will see additional Ascians come and go just like Nabriales. And come next expansion (assuming again we don't visit the North East) we will finish them all off in the 4.xx series as well as completely uncover the areas of Eorzea.

Then in 5.xx we go to a new continent.