Edit: Did Jack know that Desmond was in the Hatch when it imploded? He seemed confused by the question...
Yes i noticed that aswell i wondered why he didnt speak up all those who have been in the hatch knew about its magnetic force.....
I dont think there will be a rush to get off the island if there is a chance people could die via time travel of the brain...... but maybe theres a reason ben & co travelled via the submarine or there could be certain cordinates to travel to be safe