Many web properties are no longer accessible due to M&A activity and Small/solo publishers unable or unwilling to maintain their assets. Archives like WayBack Machine mitigates some of the loss of digital content so long as the archives themselves are still maintained.
Will spinning rust be as durable as Microfiche?
Not sure how long microfiche lasts for but someone posted a link here not too long ago about how record companies had embraced magnetic hard drives in the 1990s to store music masters and are starting to find that the drives are no longer readable.
CDs and Laserdiscs are also seeing bitrot. The layer of material that is etched does degrade over time. Error correction helps some, but if it's a writable CD or DVD it's only likely to last a decade or two. M-Drives are CDs that are designed to retain their data for about 1000 years and can be writable by specific consumer drives. Not sure how long the professionally pressed CDs last but it's not that long.
yeah those are the ones I'm referring to -- if you're archiving something like family history or data that needs to be good for centuries (without having to re-copy and juggle), those are a better choice than just about anything else.
Alternatively, tell people that they can't store something and you're likely to find it robustly mirrored by many.
Digital makes it cheap and easy to have multiple in many locations. While any one media may fail, you still have a copy - I have on this computer all the data from whatever computer I was using 15 years ago. (most of it I have not looked at in 20 years and I could safely delete, but it is still here, and on other backup systems I have)
These days your photos are probably backed up by facebook, google, or are such major players. (there are a lot of privacy concerns with the above, but they do tend to have good backups)
You make a good point about the lack of durability and instability of many types of chemical photo processes (especially color negative and print processing). I do think many digital formats will be lost to time when a color transparency or b&w negative will still be viewable without much aid into the future.
One of my favorite photo books is the re-photographic survey project by Mark Klett. He went around re-capturing the exact locations (and camera position) of notable images of the American West from the early days of the US geological survey when they had a plate photographer on the team. We are talking about a time period just after the US Civil War. So we see a landscape captured in time 10 decades or more after the original.
I've been a pro photographer for over 30 years. All my earliest digital work is archived in RAW so I have the original shooting data. It all triple backed up and I have a friend that allows me store one of my backups at his home. I've been amazed at how many photographers lost track of or throw away their older work. I'm still licensing my work hundreds of times a year and some of this older material is becoming even more valuable simply due to scarcity. The redundancy of digital is great of you take archiving seriously.
Yet, I still have drawers of original film from the late 80's - to early 2000's I'm scanning a few but will probably let many be disposed of . . .