I might be grasping at straws here. Sayid tried to kill flocke, kinda like that name , and failed. Ben killed Jacob and succeeded. Could it be that Ben is the only one that can kill flocke?
Could be that his "demise" was to join up with flocke and thus cause the demise of the island and possibly the world. Since he chose to stay at the beach, maybe allowed is a better word, he could very well be the salvation of everyone.