This plane-crash adventure series has been our constant for six mind-blowing, rule-breaking seasons. But now it all comes to an end and we’re already feeling lost without it. Naturally, we have a boatload of questions going into the 2.5-hour finale (Who will survive? Who, if anyone, will get off that blasted island?), but they probably won’t all be answered by the time the credits rolls. That’s OK: We’ve become used to that. 9 Sunday, ABC.