Actually very true. I remember that we lost all our private messages on WOS when Lee migrated forum engine to another one.Indeed you can never guarantee an online resource will always be there. If something is that important to you maintain an offline copy.
And I'll tell you more. Maybe I'm ageing, obsolete man but I completely don't get this current trend of holding all your important files in some "cloud", on some online service which can disappear any day without any notice and which is managed by some anonymous guys who have access to my data even if they claim they don't. I just prefer having everything on my hard drive + 2 or so backup copies.