Lindelof and the author whose book season 1 is based on have outright stated they're never going to answer why the departure happened. Other stuff is explained.
Not explaining the departure is IMO the correct decision as it's either the rapture or aliens. The show is about the effect that event had on everyone that remained, the cause is essentially irrelevant.
The chief's daughter, strawberry float me. If there's a more whiny, annoying, sour-pussed banana split on tv then I haven't seen them. I hate her so strawberry floating much. What the strawberry float is WRONG with her?! And that stupid expression she CONSTANTLY has on her face and ALWAYS with her top front two teeth showing.