The captain fires Keamy's gun to get his attention and says 'fixed your gun' then he fires it again as he is shot by Keamy. I would say Michael can't be killed yet. The same probably goes for Charles (since Ben said that they both know he can't kill him) and Locke (because the island keeps healing him and Ben says something about realizing now that it was pointless to try to kill Locke). So can Ben be killed? Why can't Charles be killed? I don't know why the island would protect him.