Adjusted for inflation, AOTC's gross works out to about $925m. I think ROS should finish ahead of that, given the lack of any particularly strong competition in the weeks ahead - unless Jumanji: The Next Level and/or Frozen 2 rebounds over the Christmas period.
This is true, but I remember reading twitter discussions with one of these box office insiders where he convincingly argued to adjust for inflation (which takes into account average ticket price) is actually flattering to certain movies nowadays, since things like weekend premieres, premium screenings, 3D etc. are more common than the average for blockbusters like Star Wars.
So that's what I'm basing myself to assume $1B, which still seems doable, might actually not be enough.