If BlueSky banned you tomorrow what is the plan? If BlueSky went bankrupt tomorrow?
I figure there are other AT compliant products that you can switch to but a lot of data would go missing?
And of course there are several implementations and hosts for relays (the gossip nodes), PDS implementations, clients, and appviews (the server backend for bluesky the web app).
So strictly speaking if bluesky imploded tomorrow you could just use a self hosted version of the same app or use someone else's (such as https://zeppelin.social).
The PLC directory is still technically in bluesky's hands but is being transferred an independent foundation atm and could be trivially forked if needed. And of course if you use did:web that doesn't apply to you and you just depend on DNS.
So if there's a large scale exodus from bluesky, as long as full backfills of the network exist, you'll be able to reconstruct your CAR files, etc even if your PDS dies.
So yes if they die all the comments disappear but people can reconstruct their history and move it to other PDS like blacksky, northsky, or others who are getting ready to start onboarding/open enrollment.
TLDR it'd be a bit rough if they died overnight but if it was a slow death and people had a bit of warning you'd see people move on to other PDS without issue.