Moral of the story: When you build an online community using someone else's servers and usage agreements, you run the risk that your group's use of the online space can be cut off or prescribed by the company that is hosting you. The thousands of hours spent posting content is also in danger, unless you have back-ups of everything.
I've heard similar tales of woe from people who cancelled their Flickr account, with thousands of photos in it, then found they couldn't reinstate the account. "Account deleted" meant exactly that.
Fortunately for the KM group, Yahoo still had everything stored on its servers.