I get notifications of posts in various LISNewsters' journals. I want to read them, but not necessarily the day I get the notification. Sometimes I click on the link and find it's gone. http://www.lisnews.com/~Bibliofuture/journal/2749 is one that was sent to me on Feb 9. Today's the 19th, and it's gone! Why delete it? Heck, why post it if you found it so deletable within 10 days? I've had this happen with other posts by other posters (I'm not picking on one person, in other words).
Here's my suggestion: if you think a post will be transient, put in the subject line "(Expires in 5 days)" or something like that. At least I won't be surprised if I don't get to the post in a very short time.