20TB of music and movies? How many of those could be downloaded again tomorrow? My guess is "most." The only thing that's really "mine" on my computers, and not backed up, is my own pictures. I upload those to image sharing sites on the internet. Most docs are done on Google Docs for portability reasons, and other things I've created are already on Dropbox.
I experienced a catastrophic hard drive failure a year or so ago. After replacing the hard drive, and about one day of downloading and installing the programs I needed, I was up and running again. It took 24 hours to download enough of the series that I was watching to pick up where I left off again. And if I ever get a hankering for watching something I've seen before, well, I can get it from the internet again in a matter of hours or days.