Where Are Michael & Walt?

If you pay close attention during the surgery scenes in "Not in Portland", just before Jack accidentally nicks an artery in Ben's back, Jack asks Tom why, if The Others could leave the island, didn't they take Ben back to the mainland for medical attention. Tom starts to tell Jack that ever since the sky turned purple...
Clearly, the timing of the nicked artery crisis is a red herring to distract us from that revelation. Obviously, Tom was going to say that, ever since the sky turned purple, The Others can't leave the island. This must be because the machine controlled by the button in the Swan hatch made the wormhole work.
Children often being more observant than adults, my son looks at me and says, "I bet Micheal and Walt couldn't go through the wormhole." He's right, of course.
In Live Toghether, Die Alone we see The Others holding Jack, Sawyer, Kate and Hurley on the pier. They let Michael and Walt cast off only a moment before the sky turns purple. They wouldn't have had enough time to escape. My guess is, much like Desmond, Michael will travel along the heading Ben gave him (325 degrees, or slightly North of NW) for about 2.5 weeks, only to return to The Island.

Wait and see...