npub1g2…37r9f on Nostr: I don't think so. Your message gets from your client to a relay, which relays it to ...

I don't think so. Your message gets from your client to a relay, which relays it to another relay and so on if I remember correctly. So as long as one really has your message, I don't think there'd be any loss. However, I'm sure at some point messages might disappear, I don't really know how much information retention can be done by relays.