The only chink in this theory's armor for now is whether the Night King himself is even showing up to the Battle of Winterfell. As we see in “Seven Kingdoms,” the Night King’s apparent generals are on the front lines, rather than the ruler himself. Promos have yet to show him, or Viserion swooping in battle, while Dany has definitely been spotted swooping into the fight on Drogon. Maybe the Night King heard about Arya Stark and decided to sit this one out?