I'll point out that Botlzmann brains are only something you would ever think about in a universe going through a graceful heat death rather than the equally likely big crunch or big rip scenarios.
Dark energy suggests that a big crunch is unlikely.
A big rip, on the other hand...
Last I read, there is too much uncertainty in measurement to tell them apart. It will have to be resolved theoretically, since a heat death will only be the final result when omega exactly equals -1.