I found this about them:
Wednesday, January 31, 2007
Question: What happened to Rose and Bernard on Lost?— Susan Houck
Ausiello: They're suffering from that dreaded TV affliction known as backburneritis. Luckily, Damon Lindelof says their prognosis is good. "We will be seeing Bernard and Rose again," he says. "But because Sam Anderson and L. Scott Caldwell are working actors — she had been doing a play, he's been doing TV guest spots — you have to find that serendipitous moment when both actors are available for the same episode. At the same time, I feel like if we had done Bernard and Rose in the first six [episodes], people would cry foul. Because it's like, 'Why are we seeing Bernard and Rose when we're not seeing Sun and Jin and Charlie and Claire?'" He's right: We would have given 'em hell for that. (BTW, I watched the mid-season premiere last night, and Elizabeth Mitchell should make room on her mantel for that Emmy.)
Source:
Ask Ausiello | TVGuide.com