I think widmore and MIB are on the same team.
1st thing i have noticed, this is really the second time they have tried to group everyone together and kill them. The freighter was very similar. packed with C4, widmore was trying to group the candidates together on the boat then blow them away.
Another thing, When jack pushes MIB in the water, at the dock, As soon as he doe it people from the trees start shooting, like they were there the whole time waiting for the order to attack
The plane was wired by Widmore, locke know about the plane being wired with C4. Thats why he grabbed the watch before going on the plane, he then went directly where the C4 was, and unhooked it to rig the bomb. It was part of the Con, To make it look like MIB is on the same team to everybody trying to leave the island.
He knows all the candidates did not die because he cannot leave the island yet