I think there is plenty of closure in the DA franchise where the main characters are concerned. Although I did not care much for the character of Hawke and the story of Hawke, I did appreciate it and the colorful adventure it offered. The story ended, Hawke's origins were discovered further in DLC, and she rode off into the sunset to do whatever other adventures call her. That's the thing. Being told Hawke or the Warden disappear/venture off is not lacking closure. It is telling that there is another adventure, something else afoot, in the future of the franchise. The current chapters of their lives, that which is set in the time of DA:O for Warden and DA2 for Hawke, comes to a complete close with the ending of their games.
It is somewhat akin to saying that my highschool years were a distinct adventure, one that had closure once I graduated. I leave with friends and family, and everything is roses and successful. That does not mean, however, that my life suddenly stops right there. Or that the roses and success continues forevermore, and I have nothing else further in life to pursue. After a time, I embark on the college adventure, then the marriage adventure, then the economy crisis home ownership adventure, and so on and so on.

Point is, we're just seeing a clip of a person's life during each game. They don't just retire and stop living after that point, or stop being a hero. The world still has many battles, adventures, and distressing crises to see to.
Those that are uncomfortable with a story telling you that your character goes off and disappears or moves on to adventures yet unknown/untold, I can understand and empathize, sure. Some people may have it in their minds that 'this is my character, and she would stay in Kirkwall as the Viscount no matter WHAT!' Maybe saving 'Hawke disappears' to be part of the narrative or commentry present in DA3 would've been better, thus allowing players to entertain their dreams for their character after DA2. But alas, it is what it is. Something is brewing in Thedas, and it's just saying there is a reason.