I should probably clarify that the concept was introduced in the novel by Tom Perrotta (who is co-writing and adapting the series with Lindelof), and no explanation is given there for The Departure either. Ever.
People disappearing isn't really the point of the book or the show anyway. There are mild supernatural elements, but nothing like the insanity we saw in later episodes of Lost. Honestly, the only thing the two shows really have in common is telling personal stories that focus on a handful of characters per episode.
Bookmarks