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.