"How much cognitive change can occur with a samadhi/moksha/satori experience? How healing is the single experience devoid of ongoing meditation?"

I am probably not the one to be answering these question. I only write from my experience, although I have had some wonderful experiences.

From my experience, a single experience with Samadhi was life altering. A few large, and many small. One can meditate for a very long time, if not a lifetime, without ever experiencing Samadhi I think. But from what I have read, even if the benefits from meditation are not life altering, or even obvious, people do seem to experience change from ongoing practice. I am not sure I would say that that is true for me, but I think that the benefits from meditation may be more subtle. It is Samadhi that has altered my life.

As my guru has said, big Samadhi, small Samadhi, meditation, contemplation, it's all part of it.

From my experience, I tend to think that there are some minds that are super-meditators just like there are great pianist and chemists. I'm not one of them. I just got lucky.

"Some 40 years ago I had a startling encounter with an unanticipated reality while experimenting with LSD. The observation of timelessness and the recognition that "I was not what I thought" has indeed left an impression (to say the least about it). Though the experience was meaningful, it failed to save me from regressing into self-delusion and egoism. The schemas support our neurosis. Is the neurosis restructured upon reentry?"

Neurosis is restructured upon re-entry, and sometimes some of the change seems lost over time. That's my experience. But even when it seems lost, I have been left with the memory of the experience that is also life altering. I remember the feeling of tremendous love and well-being. I can practice going back there in meditation. I can develop it in my life. I can play with it in meditation/contemplation and make if more of me, and that is what I do.

I find that meditation does what psychotherapy tries to do, but can't. No one can know from the outside looking in what is happening in another person. Often, it's not obvious to ourselves; Samadhi makes it known. That's the brilliance of the mind in meditation.

The answer is always found within.