My job involves archiving digital images on a large scale [for a famous UK library]. It can be done, and done well, but it isn't cheap, and it needs to be done deliberately, iyswim. Migrating data to new media, keeping hard drive arrays powered up, or tape robots maintained, running power to data centres, and so on. That's an active task. However, for what it's worth, I had cause recently to retrieve a load of images shot in the very early days of digital imaging of cultural heritage objects [stuff from large format scanning backs], and the files are fine. The percentage that had any data corruption at all was tiny, and I suspect they were corrupt before they were archived. The image quality is pretty good, too. Not as colour accurate as more recent stuff, but pretty good for digital images that are nearly 20 years old.
With well processed film, or prints, assuming they are left somewhere without extremes of environment, there's a decent chance they'll still be usable, even if no-one has actively looked after them.