Now, abdo0000 makes some interesting points here. It's true that it's Hot Pie who lets Arya know that the Starks are back in Winterfell, forcing her to change course. Originally, Arya was on her way to King's Landing to kill Cersei, but instead she decides to go see her family. While that decision leads to the death of Littlefinger , which, good riddance, it's true that if Cersei was gone Jon Snow wouldn't have gone on a mission to capture a white walker, which likely means the Night King wouldn't have been able to get Viserion. You know, the dragon that takes down The Wall.