For the last time... (SPOILERS)
I'm sorry for getting upset about this shit, but THEY WEREN'T DEAD THE ENTIRE TIME, AND THE ENTIRE SHOW WASN'T THEM IN PURGATORY! For some reason, everyone I talk to who has heard of this show or seen this show is for some reason under impression that the last 10 minutes of the show revealed that everything we have seen since the very beginning was after the plane crashed. That they all died in the crash, and everything occurred in Purgatory. I'm sorry, but I don't know why so many people believe this when Christian Shepherd made it abundantly clear to Jack at the church what had happened. And if it wasn't clear enough for you, then let me try to simplify that more for you.
Everything really happened except for the flash-sideways of Season 6. The flashbacks of Seasons 1 through 3 happened. The main events happened throughout all 6 seasons happened. The flash-forwards in Season 4 happened. The time travel of Season 5 happened. The only thing that didn't really happen was the flash-sideways of Season 6. The finale of Season 5 didn't create an alternate timeline or change anything. They got transported back to the island from 1977 to present day in the Season 6 premiere and that's it. They tried to alter events, but instead closed a time loop. The whole flash-sideways segments were the only events of the show that occurred in Purgatory after everyone has died. I know to some it still counts in their argument that everyone was dead and in purgatory the whole time, but the flash-sideways segments in total contributed to probably 5, 6 maybe 7 hours out of 121 hours the show provided. So, if you want to get technical, about 4-6% of the show was set in Purgatory. The other 94-96% HAPPENED.