The thing to remember is, if you can, always put up a notice saying "Go to <wherever> for up to date information", rather than removing the site completely. Such sites are interesting historically, if nothing else.
The other thing to remember is that it's not just RISC OS sites that lie dead - sites on any number of subjects do. It's because we're such a small market that there's such concern about it, I suppose - and I agree that people should take any opportunity to point people towards new information. But I can't find myself getting too concerned about it, I'm afraid. Sorry.