The issue isn't just that the media will decay, it's that the media is too cheap. There is no incentive to curate our documents, and we will end up with so many still in existence, no-one in future ages will have the inclination to wade through the rubbish.
When people had paper photographs, they soon accumulated boxes of albums, and by 1990, those holiday snaps from 1970 were kind of dusty and not worth keeping. So people chucked them out. But of course they looked through them first and kept a couple of photos, maybe even got those framed. All of which means that when they died in 2010, their kids had only maybe 100 photos to look through, and decide what was worth holding on to.
Now, our holiday snaps are uploaded to the cloud. They aren't a nuisance, and we never get rid of any. When we die, maybe our kids will be able to get a drive or an account key, or something, with 20,000 photos on. Do you really think they will do more than look at a few random ones, before adding them to their own 5,000 photos?
Same with our emails, our whatsapp messages, our blog posts.
The total amount of media from our age will still be significant - the sheer quantity produced ensures that much will remain. But what remains intact won't do so because of its significance to our age. We don't bury our most valuable items in the ground for safety, or lock them in huge chests, or keep them in safes.