In "The Dragon and the Wolf" (Game of Thrones, S07E07), Westerosi armies are seen marching towards Winterfell in order to stop the army of the Night King.
But why would they march there in the middle of the winter? It's already been established that regular armies don't fare well in winter conditions while the army of the dead doesn't care about the cold. Couldn't they simply evacuate their population down to the south and deal with the dead around the region of The Neck?