Yea I have a hard time believeing that Walt is dead. We seen Walt Leave the Island with Michael. He may be dead now but when he was seen on the island I dont think was because of him being dead. Walt is special and has shown that he possesses some sort of pheonaminal power to be here and there all at once.

I think that maybe Walt and Michale were given A place of thier own to stay. An island of thier own so to speak. Ben promised Michale that him and Walt could "Go Home" but do we really know what home really means? Could be that Ben have them a new home. Who knows there may be other civilization