Does anyone else think Ben or at least Jacob, is pulling a long con? The thing about a con is making someone think it was their idea. MIB wants to destroy, possibly sink, the island.
Jacob visited Widmore, Widmore returned to the island for a specific purpose.
He told Jin in MIB leaves, everything ceases to be. If he truly believes that, why did he so easily give up the info about Desmond when MIB told him he'd spare his daughter.
I think he came back to die. He knew Ben would shoot him as he was spilling the beans to MIB.
Did Ben also know how this would play out? Maybe that's why he couldn't kill Widmore before now.