According to an article on GameInformer, as well as several Tweets from his personal Twitter account, lead writer David Gaider has left the Dragon Age franchise to write for another Bioware IP, though which specifically is yet unknown. Writing for the Dragon Age franchise will be taken over by Patrick Weekes. Full details on his departure are available in this article.
UPDATE: Patrick Weekes will NOT take over characters previously written by David Gaider, as seen here. https://twitter.com/PatrickWeekes/status/573218932720459778