During my own personal LOST rewatch, I believe that Team Darlton has left us a clue as to the fact that Locke is actually still alive. This clue is in the form of Charlotte Malkin!
From the lostpedia article:
Charlotte Malkin supposedly drowned but came back to life while Dr. Ian McVay was performing an autopsy. McVay was told that she had spent two hours in the water. She was brought to him "dead". When he began the autopsy, however, it appeared she came back to life, as documented in an audio recording (which includes Charlotte mentioning John Locke by name).
She stopped Eko at the airport to deliver a message to him from Yemi - she claimed to have seen Yemi while she was "between places", after the drowning incident. ("?")
She mentioned TWO characters that have been posessed BY NAME. And she came back to life herself! So those three characters must all be in the same category. And Charlotte Malkin still acts very much like herself (I assume) so John Locke and Yemi are both still very much alive!
However, there is counter evidence. Yemi tells Eko "I am not your brother" and unlike Yemi and Charlotte, Locke's body is still there.