I have seen a lot of people in different posts with the same confusing questions and also there predictions so I figured I'd blog about it. I agree with some people that MIB taking the Ajira Airplane or the Sub to escape the island would be really unsuspenceful after so much hype has been put into this character. A lot of people say, (Me being one of them not so long ago), that if MIB wanted to leave the island all this time he could have gotten on the sub pretty much anytime and why did he just decide to go now. My guess is that Jacob kept him on the island and that he couldn't leave until he had a permanent body that he could live in (Lockes body. However, it seems strange that a person that can still turn into the smoke monster on the island even while being in Lockes body could finally be able to escape via any form of transportation. My guess would be that he would just lose his abilities when he leaves the island. However, I don't know if turning into a thing of smoke could even be considered just some ability, plus that fact that Lockes body isn't his so it seems weird that he could return to the real world in that body. So I gave my two sense, what do you guys think about Locke wanting to leave so easily off the island. (after all it could just be a big con to gain supporters since almost everyone wants to leave)
Also another thing, I feel like MIB was a lot more interested in getting revenge against Jacob then going home. Perhaps that is because he couldn't go home until he did, but it could also be that he is just so angry that he wanted to ruin Jacob and now that he is gone he has nothing to do.
(My apologies about jumping between MIB and Locke through out this post, I meant the same person the whole time ha)