They were last seen in the 1970s. They may be dead or may have flashed back to 2007. Their fate is currently unknown.
Another possibility being bandied about amongst fans is: fi Rose & Bernard remained "trapped" ( for lack of a better term) in 1977 - they end up in the caves as... "Adam & Eve" -the partially decomposed skeletons Jack and the others stumble upon in the cave. A big hint to this is the black & white stones found by Jack. Also Hurkey's comment in "The Lighthouse" about them being "one of us"... (aka: one of the 815 survivors)