In the realm of master copies for films the issue isn't so much DRM as merely encryption. There's likely to be some pressure to ensure that the master is "secure" from "thievery" regardless of where the bits physically reside, which will probably manifest itself in the use of strong encryption. Which, of course, brings up the question of what happens when the files are still around but the encryption keys are lost.
The bigger problem is the classic fundamental problem of data retention. The people responsible for retention probably do not value the retention of the data independent of other developments to be of sufficient value to guarantee that retention with robust measures. For example, they could leave unencrypted copies (or encrypted copies with the encryption keys separate) in the custody of the library of congress. Or they could use some sort of N of M keys encryption system and distribute copies and keys to numerous individuals or institutions around the world. Etc. However, while such things would retention of the media would be valuable to the world at large even after, say, a global catastrophe (asteroid impact, nuclear war, etc.) or merely the bankruptcy of the company that created the media such concerns the company itself would tend not to share those ideals.