Despite the chilly reception from critics, the audience score at RT is sitting at a strong 86%. While the opening weekend may not be as strong as TLJ's, it's still looking like a roughly $200M weekend domestic. If it can leg it out better (in terms of percentages, not absolute numbers) than TLJ, perhaps closer to Rogue One or TFA, it could still out-gross TLJ due to good audience reception. Opening weekends as a percentage of lifetime gross is completely scattershot. Among the Top 30 opening weekends ever (unadjusted), we see opening weekends range from 26.5% (for TFA) to 50% (for Batman vs. Superman) of the lifetime gross. I doubt TROS will be as front-loaded as TLJ, but more front-loaded than TFA and R1.
Also, let's not forget that TLJ's second weekend ended on Christmas Eve, which is always a rough day for the box office. That was why the second weekend had such a large drop. Meanwhile, TFA had Christmas Eve fall on the Thursday after release, with Christmas Day (usually a good day for the box office) falling on a Friday. Rogue One had both Christmas Eve and Christmas Day its second weekend, For its second week as a whole, it had a far more modest drop of -43.3%, which is equal to or less than the second-week drop experienced by other blockbusters. In fact, it was actually up WoW for the Monday-Thursday period of Week 2, something that almost never happens for a major movie. TLJ only really started to lag behind other films with similar performances after its third week. If it had remained on par with such films, it could have reached $700M.
TROS ought to have a smaller second-weekend drop than TLJ but a larger one than TFA, seeing as both Christmas Eve and Christmas Day are in the middle of week this year. Overall, given the usual percentage of Week 1 comprised by the opening weekend for similar films, it ought to gross around $280-300M for this first week. Assuming a roughly 40% drop for Week 2, it ought to do $170-180M, then maybe another 50% drop for Week 3, adding another $85-90M. This would put it at $535-570M for the first three weeks, about 2.5% less to 3.8% more than TLJ. If post-Week 3 legs are better than TLJ's, then it stands a very good chance of outgrossing TLJ.
If I had to give a worst-case-to-best-case range for TROS, I would put it at $600-700M. That's less than my initial projections as I expected both a larger weekend and a ROTJ/ROTS-level second-to-third film increase. Still, that would be more than enough to put it in the Top 8 films of the decade domestically, and easily the #2 film of 2019. Globally, if its overseas gross can at least equal its domestic gross, then we're looking at $1.2-1.4B, though if it's 45% domestic/55% overseas like TFA and TLJ then the worldwide gross could go as high as $1.3-1.55B.