Since Desmond has these "flashes" my thought is that in the series finale he may be trying to meet up with everyone to keep them off the plane. What's happening now on the island is a flash-forward for him (and we've already seen evidence of this in his flash back episode) and in the end, he's going to try and change the future and keep as many of the castaways from getting on the plane as he can. Of course this is if the show doesn't kill him off
. But if he does keep on living for the remainder of the series, I think this is what will happen. Of course he will probably have to get on the plane or die for this to happen. No good deed goes unpunished sort of thing. So even if we see some of our favorites and not so favorites being killed off, in the end this will all be changed and they will go on to live full lives because Desmond (or perhaps some other character) will change the "future." Hopefull I'll be on this board in three years to see if I'm right!