That's sad to hear, but it makes total sense to shut down the server given its sensitive data, rather than hand it off to another person.
Mastodon/ActivityPub is a poor fit for a social network IMHO.
- Accounts should not be tied a single server and their continued maintenance.
- Private data and DMs should be end-to-end encrypted rather than entrusted with a single administrator.
- People don't want to self-host.
The core problem of a lot of social networks comes down to name aliasing, and who controls the name registry. In the case of nostr[1] this is not a problem because everything is using public keys. Another protocol is Farcaster[2] which plans to use a smart contract to maintain a name registry without requiring a single controller.