Desmond = constant
Okay, so there is my little theory about Desmond...
I remember that Faraday said that Desmond was his constant. But what if Desmond was everybody's constant?
Remember that Desmond turn the key and make the Hatch exploded. Maybe Juliet never destroy the bomb, and the reason they came back to 2009 is because Jacob died. And when the Dharma realized what can happen with the hatch, they set the bomb in the hatch and explain that if there is any trouble, they have to turn the key = make the bomb explode. SOOOO by turning the key, Desmond would be the constant (i dont know how they can explain this in a better way)
It would be him in the sub, Charles Widmore bringing him back to kill Smokey ?
Remember that, when all the losties came back, and they met at the Faraday's mother (aka ex-wife of Charles Widmore, sorry i forgot her name) , she said to Desmond : you have an important mission to do for the island, you will have to go back or something like that, she told him (in other words) that he is going to be in the season 6 !
Imagine that we see Desmond life as 'if the plane didnt crash' and at this moment all the losties meet. Showing that Desmond is kind of the constant of all these people.
Any thoughts ?