In the most recent podcast dated 4/16 D&C confirm that Nikki and Paulo are dead, buried alive.
The whole deal with Nikki and Paulo was the writers/producers effort to respond to viewer questions about the background losties.
So they introduced N and P. But the viewers hated them. Expose was a great episode IMO. It was funny and entertaining. It also gave a different viewpoint. A look back at missed characters. My only complaint is I would have rather seen Nikki dive in to the waterfall lagoon to look for the diamonds.
