Hmm after reading the posts I have a few strains of thought. If he comes back Michael will probably die because his answer the island's question would most likely be: I did what I had to do. (ala Mr Eko.) and this answer will most likely cause ol' smokey to give Michael a thrashing. Walt's return will most likely have some sort of time warp excuse because I'm sure the actor is now bit bigger than when he left.