Man, Barristan sure is out of touch with the situation in Westeros. First he thinks Balon is come, except he knows that one is dead and then thinks its Theon of all people. Not that it matters much. At any rate, I imagine that this battle will be enough to attract Rhaegal and Viserion to join the fray ( on no particular side ), cue the dragon horn being blown. What happens then is anyones guess.