I think we all have been thinking about what Dogen was trying to accomplish in the wrong mindset. If you recall, Ilana thinks that MIB is stuck in his human form for killing Jacob. Also the kid appeared to MIB and told him that he could not kill Sawyer because of the rules.
I think what Dogen was trying to accomplish is to get MIB into an altercation with Sayid, "The Candidate", causing Sayid's death which would doom MIB to a human form that would allow for him to be destroyed. So in essence Dogen lied to Sayid all along and he knew there was no chance in Sayid actually killing MIB. MIB figured out Dogen's plot immediately and was not going to break the rules and give up his powers.
I now also believe that the way MIB will be destroyed is for one of the Lostie Candidates to be killed by the hand of MIB leaving him mortal and allowing someone else to kill him. So now the real question is, who will it be: 4 is dead so that leaves us 8,15,16,23 or 42??????
MIB wants all of the Candidates to die by fighting each, accept a wish from him or join him by accepting him as their leader and then he will be free forever because all 360 Candidates will have failed to have what it takes.