After alot of thought I have figured out how lost will end.
Infact we have all seen how it will end. You remember in the season 4 finale when they showed us the first flashforward, we all didnt realize it was a flashforward until the end.
We are seeing how the show ends in these alternate realities.
"It only ends once...everything before that is just progress."
How it ends, is the alternate reality. In the alternate reality everyone is off the Island, and the Island never existed.
I believe in the season finale, whoever the candidate is will destroy the Island thus leading to the Island being suck and MIB getting his dream. Going home, being a human, on the real world.
Thats why we see Doneg and Ben in LA in the ALT because one the Island is destroyed, they all never went on the Island.
Its not that tricky, think about it, whoever the candidate is, will by choice, (remember everyone has to do everything, willingly) he will destrouy the Island. and that is how the loop and the game ends. And once that happens Everyone on 815 lands safely, thus the Island never existed.