It may be that given the essential nature of consciousness as being radically subjective, that there is no objective proof of its independence other than direct subjective experience - such as an NDE.
but I would add that in areas like this where unprovable (or at a minimum unsupportable) assumptions must be made to underpin one's argument, we might consider avoiding making absolute statements, and should certainly avoid making these topics a part of our central "proof". Not to do so undermines the credibility one's whole argument and reduces the discussion to a comparison of "faith" systems. And in the end, talking about faith will not help us reach an objective understanding of the nature of our being. We have seen lots of examples of that in Alex's discussions with those who have no interest in logic or proof, and are happy to just express their particular belief system. Let's not make that mistake ourselves.