DRM free ebooks would/will never just disappear! I attempt to put my money where my mouth is and buy DRM free whenever possible, and consider carefully buying at all if no DRM free copy exists.
And it's not true that "ebooks would/will never just disappear"; if you don't proactively care for the health of your storage media, they will fail; from an archival point of view most storage media will almost certainly fail in short order (years, decades at most). I have piles of CDs, floppy disks and hard disks lying around but I am not confident I can access all the data. Rather, I'm sure only a fraction of the files will still be readable.