That's true only if all these are true:
* The bits are being refreshed on a timely basis to prevent bit rot (storage on a single USB stick probably won't last 10 years; a DVD maybe 20).
* The image is regularly copied to new media.
* Someone or some entity (e.g. cloud storage provider) continues to ensure the images exist on the servers, media, whatever.
* Someone sees value in preserving the media on which the images reside and pays to keep it there or copy it to new media. A print in a shoebox is immediately viewable and can be kept or tossed. A USB stick or DVD in a drawer cannot be viewed unless someone in the future has the interest and means to view it.
* The format that the image is in has to be readable in the future by some program. Will .NEF, .PEF, or .RAF files be viewable 100 years from now?
All of those things are a concern. But, digital archaeology will exist. Technology will exist to extract information off those devices. But in the short term, our digital photos are only viable as long as they are kept moving. So as long as we're alive, we have the job of making sure this information is copied into a succession of media. But after that, it's in someone else's hands. Just like whatever shoebox you'd throw some prints into. The sad fact is, the majority of photos will either go into a landfill or evaporate slowly from digital media. The much touted 500 years for paper is under ideal conditions. Someone has to care to retain those documents, they have to be worth something. It's the same with digital images.
Since we're talking about the very long term, there's no way of knowing what might be buried for a time then resurrected. Twenty-year-old media might be very hard to recover, and 500-year-old media, trivial. Most likely, no one's going to bother unless there's the perception that the information has some value. I bought a small box full of photos, 3x5s mostly, at an estate sale awhile back. I had the thought of scanning them in and sharing them online. I haven't quite gotten around to that. The chain of custody that made those images meaningful has been lost. I don't recognize any faces. Very little is labeled, or with scant text, first names, years. These photos are worthless without context. What difference does it make if I pitch them in the trash or the paper lasts 500 years. It doesn't matter either way. If the family who had these were willing to sell for $5, how much are they worth when I'm gone?
Bitrot is becoming a more recognized problem in the last few years. Of the image formats you mention, I know most NEF types are supported in Open Source software, so that is at least documented. Likely, those formats are documented elsewhere. Taking the very long view, these are encrypted files. Even a completely opaque format could be reverse-engineered today or in the future.