Their current films (mostly Dory) should be good for at least $500M more, so basically, their slate for the rest of the year will need to cumulatively gross $1.3B (or a bit less) to break the record.
They still have Pete's Dragon, Doc Strange, Moana, a few small films, and whatever Rogue One can do in those first 15 days.
It's impossible for them to miss the domestic record at this point. Moana, Doc Strange, and three weekends of Rogue One aren't going to cumulatively gross less than $400M, even if Dory's legs are worse than expected and the rest of the films gross $0,