What's really annoying me right now is Jack--does he really think that if he detonates the bomb, that his consciousness will be magically transported to 2004 on a Flight 815 that never crashes? (And with or without the memories of the past five seasons?)
I personally don't believe that he can alter the timeline--but even if he could, why does he assume that he would flash ahead 27 years into the future of that altered timeline and live life as usual? If he survived the blast, wouldn't he just remain in the revised 1977 and live out the rest of his days on the island (content with the knowledge that eventually, the corresponding alternate timeline/future/younger version of himself won't crash there since he changed history)? I can accept his being willing to sacrifice his life so that the future version of himself and the others in the 2004-B that he's trying to create will never crash--but that still leaves "current" Jack and Sayid and the rest stuck in 1977-B. (Apart from any magical vanishing act, which I just wouldn't accept.)
At any rate, I guess that in the finale we will see:
1. Jack's plan failing, allowing the Incident to play out as it was meant to, resulting in the creation of the Swan and the crash of 815.
2. Jack's plan succeeding, but ironically and inevitably still creating the Incident and guaranteeing that history will play out just as it was meant to (as with Sayid trying to kill Ben but only turning him into an Other). So it was Jack's fault that the plane crashed! How guilty and responsible will he feel now?
3. Jack's plan succeeding, with no Swan station and no crash of 815.
But where would the show go from there? They might just leave us with a mushroom cloud, so we can wonder for nine months how the show is going to continue as it reaches the final season.
Or they could defy logic, go with #3 and end this season with a scene of 815 landing safely in Los Angeles in 2004, with the passengers getting off as total strangers and going their separate ways because Jack's plan worked. I have no idea where the show would go from there.