I know psychedelics have been used successfully to help the terminally ill come to terms with impending death. Using LSD might therefore help those on their death beds accept death and allow them more easily to choose the inevitable and go willfully into it.
My, I think very plausible, speculation is that using LSD on one's death bed would only really influence the last stages of fully conscious life (and since that's the only thing we know from experience and can be sure we influence, LSD's affects on our fully conscious selves are what's relevant when considering the decision agnostically). The experience of the brain shutting down over 3 or 4 minutes in a succession of stages due to the the loss of oxygen and glucose needed to maintain coherent holistic activity will likely be of too subjectively radical or just plain chaotic a nature to be noticeably affected by a psychedelic. And of course, if anything survives brain death it won't matter what's in our brains as they shut down. Plus, most "natural" deaths involve great pain from whatever you're dying of -- and if you're in the hospital, tons of drugs -- just prior to cardiac arrest, so there's likely to be unideal cognitive interference going into it anyways.
I also don't see why a brain would have the resources to spare to create a profound or comforting transitional phase into an afterlife realm it has no experiential familiarity with when the "cognitive miserly-ness" that characterizes the brain's activity all through our lives suggests it would just go unconscious (which wouldn't be "bad" at all, would it, so why bother? If what our fully conscious personalities are is what continues then when our unconscious brains cease functioning we'd just suddenly be experiencing the afterlife like if our brains had been obliterated instantly from a fall, bullet, or car accident). Why not preserve the energy needed for this theorized "last fireworks show" for maintaining more basic functioning (as alluded to above, there is NO EVIDENCE to support the DMT release "hypothesis")? To the best of my knowledge, knowing one is going to die is a reflective conscious realization, and during non-instantaneous death the cognitive faculties that would allow us such realizations (along with the faculties that allow us to experience anything so high order as mortal fear or despair, or to regret using LSD on our death bed) likely leave us a substantial time before the end.
(or at least when it is stated matter of factly)
