Actually, NDE researchers have done all that--- but within the narrow band "near" death but obviously prior to irrevocable death. But yes, it is not actual death, which is why they are called "near death" experiences. But the point is not that they are in fact actual representations of what happens when we pass the point of irreversible death, rather the point is that with diminished brain function, there is an incredible experience some have that is unlike other experiences (dreams, hallucinations, etc.). It is merely one part of a growing challenge to the physicalist notion that consciousness is produced by the brain (example include terminal lucidity, hydrocephaly where people with 5% of the their brain function normally; etc.).
Of course, a more relevant discussion might be had by digging into what Dr. Greyson's DOPS colleague Dr. Jim Tucker has recorded with respect to past life memories of young children, including intermission memories from death to rebirth.