Nostr: How portable is my Nostr content if a client or relay shuts down?

Short answer

Your keypair is independent of one client, and signed events can be copied to other willing relays. Portability still depends on having the key, an archive or surviving relay copies, compatible event support, and working links to any external media. Back up important posts and files yourself. A single relay going away need not erase your identity, but it can make older content hard to find.

Sources

NIP-01: Basic protocol, NIP-02: Follow lists, NIP-65: Relay lists, NIP-94: File metadata.