Dude, I totally agree with this - the only thing worse is when an entire archive goes 'poof!' :(

In hindsight I always think 'I should have saved it!', but it never occurs to me until it's too late. As I'm reading, it never occurs to me that the story might go away some day. I think it's like you said, we are used to the idea of published fic - always available in some way or another.