@lewm
I'm less sure of this, but I don't think digital copies of anything will last forever
All physical media have a finite life, due to the second law of thermodynamics - on average, disorder increases in our universe.
in addition to general decay, vinyl records wear a little each time they are played. We don't really know how long CDs and other silver disks will last - they have not been around that long - say half a century. There have been a few instances where the reflective layer has oxidized, but this seems to be down to faulty manufacturing.
The problem is worse in the film industry where acetate tapes, apart from being highly flammable, disintegrate within a human lifetime. For this reason, the National Film and Sound Archive of Australia is digitizing its collection. Often the archival copy is on CD-like optical storage.
A bigger problem is that while the media may last for a very long time, the transports needed to read that media become obsolete quite quickly. There was an industry joke that next year's optical media are made from the holes cut from last year's optical media.
The only 'fact' I am sure of is that a new copy of a digital source should be identical in content to the original because of the extraordinary error detection and correction schemes that are available. So a digital source can be copied forever, even if it consumes many generations of media
