Hello,
I can't help you too much with psychedelics because I don't use them. Only once I had hallucinations with narcotics and it was not very conclusive or even frightening: the feeling of being manipulated from the start, that my life had been created in a laboratory and that I was artificially kept in life in a test tube.
However, I can give you my point of view on the evolution of my beliefs with the approach of the CTB and with the SI. I never believed in God or an afterlife. For me there is nothing except the universe.
However, I am sensitive to the issue of NDEs. I didn't experience one in the clinical sense of the term, but I saw myself dying. I saw a great white light, and I felt propelled towards the sky. An angel silhouette was waiting for me and I felt a sense of fullness, peace, happiness and perfect love. Even if I'm very Cartesian, these experiences can help put death into perspective and say that it's just a sweet passage. Today I can't wait for my CTB to relive this experience! I keep thinking about it and wanting to go back for years.
Also, from the moment the CTB got serious, I felt the compulsive urge to go to church. I learned a little on the subject and even if that did not change anything with my beliefs, I reconciled myself a little with the religions. I even find a lot of beauty there sometimes. I feel a lot of emotions when faced with certain religious stories that echo my suffering.
For a while, I also watched a lot of reports on space, the universe can greatly relativize the importance of life on Earth. This allows us to realize our insignificance, the mystery of the universe, the beauty of nothingness and the absence of life. It makes me want to join him. Practicing lucid dreaming can also help here.
All these experiences made me relativize death. There are so many different beliefs, different experiences and beauty in death that I believe that I'm calmly approach my imminent end of life. However, I keep in mind the fact that the SI can come back at any time, it's a real inner fight.
Sorry for the length of the text, I hope you find help with your questions.