Dinklage has probably moved on. His dialogue for this game could have been recorded two years or more ago, and Game of Thrones has exploded even more since then. He's surely got better opportunities on his plate than recording more stuff for Destiny, especially after he got slammed for his performance. If they can convince him to come back before Taken King maybe they can salvage our Ghost but if they go into the massive expansion without him they may as well do it all over with a new voice actor, original content included. Can't go that long into new content with only a handful of dialogue from the vanilla game.