In the beginning, many folks suggested that they were all dead and the island was...well, neither heaven nor hell but somewhere else.
I don't think that's so. I suspect that Dharma and/or Penny's ridiculously wealthy father have spun a tale for the world to swallow to keep people from looking for the island.
Or, the authorities who search for downed planes did find parts of the plane but couldn't find survivors because the island is not visible to radar, the naked eye or anyone who isn't already on the island.
Or, the woman, if it is a woman (I'm still holding out for Sanjaya popping up on the island
) who speaks in tongues (Spanish, English, Italian, maybe Russian, maybe something else like Arabic) is a liar. Other than Hurley, who really tells the truth on that island?
Or, who knows? The answer will wind up being something so far out that no one will come close to guessing it, but it will lead to a hundred other questions.