It might not do as well, but the original pulled in $473 million and seems fairly well-received by general audiences, so unless Rock fatigue sets in, I'd put decent money on it at least breaking even. Regardless, it would be more or less in the can fairly soon, so that entry in his (potential) franchise would be off the table anyway, freeing up some time.
I did forget to mention in my original post though, that he's in Disney's Jungle Cruise as well, which is a very big deal. In the end, I think Rampage 2 coming out is largely dependent on how he personally feels, as its success (while solid), was not spectacular and the general media doesn't seem too interested in covering it. Less heat = Less chance of a sequel in this case, imo (sadly).