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.