[bewitched]

I have a glimmer of an idea forming about the sideways timeline....

Maybe the sideways timeline is life reset for all of the candidates who choose to eventually leave the island. Knowledge of the island (at least the knowledge of what the island really is) is reserved for those who choose to stay and serve the island. They don't remember the island, even though they were there because that knowledge has been erased from their consciousness (but it flits about as kind of a memory of a dream). But their lives are reset based on what they "chose" on the island and how it is reset is based on whether or not they found ultimate redemption; whether or not they were able to be "good" (which doesn't bode well for Kate, I suppose...i.e. "be good, Kate"). Jacob said everyone he brought there previously was dead...but he didn't say he killed them or, for that matter, that they necessarily died on the island. Maybe once you are vetted as a candidate, you can choose to stay and serve (and presumably not die) or to leave and live your life, with death being the only (inevitable) outcome to that life. This would also explain why the dead island people are alive in the sideways timeline. Maybe "death" on the island is really just a shift to the life you would have had if you wouldn't have been detoured in Jacob's efforts to get candidates to the island.

Does that make any sense?