The soldiers from the Vale are going to save the day, its pretty much spoiled from the preview for next episode. It an entire region of fresh soldiers, who have been loyal and loved the Starks since the time of Ned's father. The lands are fertile, the granaries are stocked, and the men full of honor. Once Sansa comes back and tells those guys that Ned Starks daughter was raped by the Boltons, that whole region is going to pissed as fuck and rally up their men. The Boltons men and whatever Northern houses loyal to them are dwindled from the war. With Jon Snow, wildlings, and possibly an Umber ruse, and a whole region of fresh soldiers, Ramsays time is close.
It looks like theyre taking Sansa to the Wall though, so I'm betting she either sends a letter to LF in the vale, or LF rallies the Vale himself.