The default outcome for any site that isn’t maintained — including the one you’re reading right now — is for it to vanish. Permanence doesn’t exist on the web.
Only 2 companies keep coming to mind: WordPress.com and GitHub. I believe both will last for decades, maybe even 100 years, and both embrace the open web in a way that most other centralized web sites do not.
Even though I self-host this weblog on WordPress, I’ve chosen to mirror to GitHub because of their focus on simple, static publishing via GitHub Pages. It has the best chance of running for a long time without intervention.
This is a really cool idea. I've never thought about mirroring my site, and since I already use Git to push updates, adding a mirror is just adding another remote.