At the start of season 5, the island is seen to be moving through time. Also around this time Sawyer is seen to get a splinter in his toe as his clothes disappear during the transition and he has no shoes. Therefore there is a possibility that his toe could become infected and then have to be amputated, leaving him with 4 toes like the statue. Therefore, possibly during one of the transitions, he could do something heroic, possibly resulting in his death. Therefore in order to remember him they could make a statue thus explaining the 4 toes.