They're funding Fig to create and run a "full network backup" solution. What Bluesky really needs to do is figure out a way to get users to own their own backup recover key, whether personally or through some third-party service.
I'm sorry, just to clarify: in your scenario where the app/company is suddenly vaporized from the face of the earth, if that happened to Bluesky right now it would effectively mean that >90% of content currently published using Atproto would be lost?
Realistically, I can't say "yes" because I'm sure there's plenty of copies of entire network by now. They would be out of date but would have all old records. So that could be maybe 70% that's already backed up. I guess they likely won't include images/blobs. There's an ongoing project to build an always-available full archive with this specific purpose (https://atproto.com/blog/introducing-hubble-a-public-mirror-...) so it is also an active area of work.
If we imagine that nobody has a full copy today or is unwilling to share it, the answer would technically be yes.
I'd still say that, for an app going down, the answer is "no" because "Bluesky app" and "Bluesky hosting" are like two separate services. The point I was making was that specifically "apps going down doesn't destroy data". (The distinction between "Bluesky app" and "Bluesky hosting" isn't completely contrived because I'd expect the cost of running the app to be many orders of magnitude higher than the cost of running hosting.)
But if you pick a hosting company, and users don't have backups, and nobody does mirroring, then yes, hosting disappearing would destroy data. As with literally any hosting.