So we know MIB has followers. But why does he need them? To fix the plane/use the submarine..yes. But, I think before he lets them leave he's going to ask for one "favour". He's going to ask them to kill 6 people (who are actually the 6 candidates). I think that without any candidates left to protect the island, the island will cease to exist. So before he leaves, he wants the island to be destroyed too. So he orders his followers to kill the 6 candidates. Sawyer will realize this and perform an act of bravery, thus redeeming himself, but he will get killed by MIB.
Illana the protector will be killed, Sun and Jin will be killed, Jack will be, Sayid will be, and there will be one left who escapes: Hurley. Jacob will help Hurley escape. But in the very end, Hurley will realize what's happened. And that the island is better off gone. So Hurley will get Widmore to kill himself. Hurley cant kill himself, so he has to get the hand of man to do it for him. And that's how it will end : D