There was a thread on Hacker News about Google closing down Google Groups and people losing their data. This is adapted from a reply I made to a comment:

I think the problem is that people haven't adjusted to the new ways of keeping data. They assume their free Yahoo account is theirs, the way their closet is theirs. You know, if you leave a box of pictures in your closet, it'll stay in your closet barring a catastrophe.

Online services are available to serve a certain set of goals and objectives. If those objectives change, your stuff might get thrown out. It's more like asking a hotel to let you keep a box of stuff behind the desk for a while than it is like your own closet. They might keep it for a really long time, but if the hotel changes management or remodels, your stuff could get tossed. Especially if you're not regularly staying at the hotel.

It's not even "you get what you pay for," because paid services shut down too. In this era of cheap storage, there's no excuse to not make multiple backups of key data. Ideally at least one physical copy of important things. Actually print the emails out, put them in a binder, and put it in your closet. Keep one copy at Yahoo, one at another online backup service, one on your PC, and one on an external harddrive. That sounds like a lot, but it's not. Once you get a sensible backup policy and figure out what's important, it doesn't take very long to do backups.

It's a sad story you shared, but not unforgivable. Someone's keeping a box of your stuff behind the desk at a hotel. You can't count on that box to stay there. Now, the problem is people haven't realized that yet. But slowly, it'll become widely known and understood culturally. If it's important enough, keep multiple online and offline backups. Don't count on anyone to hold on to your stuff for you, because if management changes or the place gets remodeled, it might not be there any longer.