[KiwiBird]

That because you are looking at the wrong candidates.
You have Roose Bolton, whom suppossedly has gathered half of the north behind him now. And then you got Stannis, who is also ready to make his move. (you can check out the spoiler chapters wich Martin has read on various events.)

Either one of them is more then enough to kick the Greyjoys out of the North when you consider that most of their forces have withdrawn and been deployed against the Tyrells.

However at the moment Roose is stuck at the neck. And Stannis will hope to gain the Ironborn alliance (Asha) in his support for kingship.