This answer: https://electronics.stackexchange.com/a/227385/43191 had a lot of comments associated with it and now all but one are gone. Anybody know why? Or how?
You've been around here long enough that you should know comments, especially lengthy comment chains, get deleted occasionally. I didn't see this question originally, but guessing from your post and people's likely reaction, there was probably a lot of back and forth between you and one or more people arguing about something.
Comments are not for content. They are supposed to be for short discussion with the author of the post. This could be to ask for clarification, a short related question, pointing out a problem, etc. Ideally, the result of comments is edits to the post.
When someone asks a quick related question, it's OK and common to answer with a quick comment. However, you should always be asking yourself whether your response (if you are the post author) should instead be a modification to the post.
We're all guilty of answering quick questions in a comment with another comment. That's OK, but alway keep in mind that comments may be cleaned up. If what you are saying is quick and dirty, then you shouldn't care if it gets deleted after a while. If it's meant to be permanent, then it doesn't belong in a comment. Modify your post instead.
The one remaining comment is pointing out a issue with your post that you didn't address. I suspect that it didn't get deleted because it's point is unresolved and still valid (the zener can't handle the power if the load is removed).