Remember the movie, Groundhog Day, with Bill Murray. He kept waking up on the same day, learning more and more about himself and how he could voluntarily change his outlook on other people. When he finally changed, sincerely, the clock started again. I don't believe the Losties, themselves, are in a Groundhog Day type of loop thing but the overall idea of that sort of thing - people are brought to the island to see if mankind can change, until they do, MM and Jacob are stuck in time, is an idea I could consider plausible. Man either has to self destruct or learn to live together for the island "clock" to start again and Jacob and MM to move on. By killing Jacob MM can ensure the self destruction destiny and move on.