It only takes one match / hard drive crash / electrical fault/ flood / lightning strike / earthquake to wipe out any archive, physical or digital. The only invulnerable data is that of which multiple copies are stored off-site away from the originals. And don't forget the role of the vinegar syndrome, or just plain carelessness. Hmmm, better get scanning then...
You know that no matter how many archives you have in how many places, nothing guards against obsolescence. When I moved a few months ago, I tossed the last of my 5¼" floppies. I have not seen a working 5¼" floppy drive in about a decade, no longer had a way to read them, so I tossed them. Even if you find a CD in 100 years that would be still readable, there is no guarantee that you will be able to find a CD drive to read it, and even if you find a drive, there is no guarantee that a computer will still have an IDE interface on it, so you could use that drive. Long term on-line storage, depends on someone paying to maintain the account, my daughter might want to continue my account when I am gone, but will her children, especially if I am gone before they are born. One thing that will still exist is the thousands of B&W negatives that I have carefully stored over the years, I have a negative that was taken of my grandparents when my grandmother was young, sometime in the 1940's according to my mother. You know I can still pull a perfect print off that negative. I have a print of my grandfather on my dad's side, that was taken sometime during WWI it's a little faded, but still perfectly visible. I have a feeling that the current period in time will be considered a lost decade, because there will be so little photographic evidence of it.