I'll see you in another life brother!! by Jesse Camacho

I believe Desmond will return to Island, for reasons unknown, perhaps because Charles and Zoe know he is special and they will attempt to do experiments with him. During these experiments Desmond will see flashes of the sideways universe and at times he will go back and forth. One or two things will happen after that:

1. Desmond will remain on the Island and continue to flash between realities, he will tell everyone what he has been seeing. Once he tells Jack this, Jack will realize it's his destiny to somehow change things and do a reset. I believe that it will have something to do with the volcano which is said to have "seismic importance". Jack and Desmond will somehow get the volcano to erupt thus burying the island. Before they die Desmond will turn to Jack and say: "I'll see you in another life brother!"

2. Desmond will still see flashes of the AU, however he will be killed on the island. Once dead, Desmond's consciousness from the island will take over that of his in the AU and he will remember EVERYTHING. He will be walking around with all these memories of something that NEVER happened, quite like "Flashes before your Eyes". Desmond will trying desperately to find a way to get everyone to remember the island and what happened there. He will also attempt to save the ones who died on the island, but because the universe course corrects itself, he will fail. He will attempt to save Charlie, Daniel, Ana-Lucia etc, however in the end he will fail. However he will also try and get his friends currently trapped in the island universe to travel to the Alt with him, where there was no crash.