I don't think Rogue One is going to have much of an effect as noted already, different set of characters in a different place in time. What will be more important though are those early reviews. If they come out saying that Episode 8 does something totally new/ is not a rehash of a previous movie, a lot of the fans that were disappointed in TFA's relatively unoriginal story direction will be willing to give the new trilogy another chance. It wont break TFA's record, but it how close it can get remains to be seen.