Lost = Prison Break?

The central question on Lost is just what is the Island? It seems to have magical properties (though they could be due to those living on it) and it seems hidden to much of the world. From the start, there's been speculation--it's purgatory, it's the Garden Of Eden, it's an alien spaceship, and so on.

I was wondering if it isn't a prison.

Jacob and his nemesis, Bocaj, both seem to live there, and have been there a long time. And we know Jacob (or some projection of him) has no trouble traveling anywhere he likes. But I don't think we've seen Bocaj anywhere off the island. We believe he's been all over the island, though, constantly arranging things.

Bocaj stated he wants to kill Jacob. Perhaps Jacob is his jailer. Maybe he can't do anything until he gets off the island. Though it's odd that Jacob keeps bringing people to the island, for Bocaj to corrupt. And ultimately (as far as we know) Bocaj was finally able to bring about Jacob's death through the latest crew. Perhaps Jacob wanted Bocaj to succeed.

But if he did succeed, what now? With Jacob gone, does that mean Bocaj can now leave? Or does he finally get to move into the statue's foot?