People sometimes have important personal reasons for deleting things but this does not mean anything. It is not as if "x posted y on twitter and deleted it afterwards" or "the page was edited/deleted, here is an archive.org link" is uncommon on HN, nor it is as if a stalker would not be able to scrap HN posts of someone instantly as they were posted.
> it disappears.
In my experience they show as [deleted] but I guess this is only for posts that have replies.