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 They would be out of date but would have all old records.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.