After reading this, you’re going to have to come to grips with the fact that I do not normally write fiction. It’s just a list, but you asked for it. Please let me know if I've forgotten to tie up any loose ends.
The light stuff and the cork in the light stuff never happens. Whitmore is not killed. Whitmore tells Jack that if Locke (the smoke monster) gets off the island, he will kill everyone since he doesn’t need anyone to help him anymore. There is no way to kill the smoke monster. Whitmore helps Jack set up another sonic fence. He also tells Jack that the cycle of protecting the world from evil with replacements is never ending, and that as long as he’s alive he will supply all the technology necessary to keep the smoke monster from destroying the world. He tells Jack that the island is an alternate reality and that there is another version of himself who has been perfected back at home. He tells him that the hydrogen bomb reset everything and that his life is on track. Jack is really happy to hear this. Whitmore tells him that he will be back and forth from reality to reality to help him until he fully understands. After Ben hears about his alternate life, he decides he is done with the island. Ben and Whitmore have a nice heart to heart and you, dear watcher, are convinced that Ben has finally given up his flip flopping ways.
Jacob tells Jack, Hurly, and Sawyer that they were not supposed to be the replacement, but that the replacement is not ready. Jacob tells them that it wasn’t supposed to happen like this, and that it has never happened like this before. He hopes it won’t happen this way for Jack. Jack volunteers to be his replacement until the real replacement (Aaron) is ready.
The flash sideways is, in fact, real. Because the survivors have been diligent in their duties to help save the island, Jacob enables them to have the life they would have had if they would have landed – with a few changes because he loves them and he wants to bless them. So everyone ends up together in beautiful harmony, Hurly and Libby, Jack and Kate, Sawyer and Juliet, Desmond and Penelope, Charlie and Clare, etc. They have a vague memory of what happened on the island that provides a way for them to continue their relationships.
The flash sideways Charlie and Claire meet and Desmond helps them remember everything. Claire has her baby and she realizes that Aaron is Jacob’s real heir. In order to save the world, they must return to the island and raise Aaron there. She asks Charlie if he will go with her and he starts crying and says, “YES!” They run into the real Kate again – who with Desmond’s help is able to remember the island also. Kate agrees to go with them to protect them and so that she can run away from her life as a murderer for good. Desmond and Penelope’s mother help them return to the island.
Back on the island, everyone, except Jack, continues to struggle to get off the island. The “real” Kate, Charlie, and Claire show up with Aaron. When Kate and Claire see the alternate versions of themselves, they morph into one person, and they can remember everything from both lives. Claire is cured from her insanity. Charlie, Claire and Kate agree to stay on the island with Jack. Everyone commits to helping Claire raise Aaron on the island so he understands his duties. Kate offers to become immortal too so Jack won’t be alone. Jack agrees and she drinks the blessed water from the river. Now no matter what happens, Aaron will have mentors to help him.
Everyone else escapes the smoke monster and fly back to LA. Desmond has led sideways Sawyer, Frank, Hurly, Ben, Whitmore, etc to the airport. The plane lands on Whitmore’s private runway. When the plane lands, the flash sideways characters meet their island selves and they morph into each other. Everyone can now remember everything. The flash sideways Jack is also there. Whitmore tells them that although Jack is on the island protecting the island (where he will never die) the sideways version of Jack will live a happy life. They tell the flash sideways Jack that the immortal version of himself is with Kate on the island, and that Kate couldn’t come back because she would have been arrested and possibly given the death sentence. Jack is happy to know about that. He can remember things vaguely, but not everything since his two selves have not morphed, but he is satisfied.
So, everyone ends up happy in one form or another. As Jack, Kate, Claire, Charlie, and Aaron start their life over on the island knowing all they need to know. All the flash sideways folks are happy and together.
And in the last flash sideways scene, Jack meets Sarah, his ex-wife from the first season. Jack falls instantly in love and his son really likes her. You like her because they meet under normal circumstances (she is not in an accident and she is not about to get married to someone else). You also know that it’s going to be different because Jack is over his fixing stage. He is able to let things be. Knowing that Jack is able to let things be is the point of the whole show – Jack changed into the person that he needed to be so he could be happy, and so did everyone else.
And then . . . the last island scene, the last scene of all, LOST ends in a typical cliffhanger. You see a small plane in distress about to crash on the island. Jack, Kate, Charlie, and Claire look at each other and smile. You know they are thinking, “Ah, more flawed folks who need to come to grips with themselves.”