Michael's inability to die or be killed is reminiscent of that of a time traveler arriving from the future. If the freighter explosion sent him to the future and he would 'later' travel back to a point in time before the freighter explosion, he could not kill himself or be killed as this would otherwise constitute a temporal paradox (The huge problem, of course, is that it would have to be the Michael from the Future trying to kill himself and couldn't explain what happened to island Michael).