desmond had the choice to marry penny and not go to the island.
however the old women in the ring shop said that the universe has a way of course correcting.
So if desmond did not go to the island the plane would of not crashed
And maybe everyone on that plane was meant to die
So if desmond did not go to the island all the losties would of died
Thats maybe why losties are dieing one by one
annd thats maybe what the island is meant to do course correct