I have read that they have been replicated with ketamine and LSD, but they also differ in many aspects, namely, the near-death experience generally having a life-long effect.
The last time I took LSD, 35 years ago this month, was an experience that's lasted me thus far: I remember it well, and I quit taking hallucinogens that day.
And the claim of people being "clinically dead" when they experience an NDE seems a little shaky, anyway. They, nor anyone else, knows just when during the "death" the NDE took place. And, as someone posted, these people are the ones who didn't stay "dead." If you do that, my bet is that you'll have no memoriies.....
™ Version 4.2