I’ll try. 😅

Your notes live on any relay to which you’re connected at the time you post it. We can assume that for some period, each of those relays will retain your notes “on disk” until such time as the relay expires those notes based on a defined retention policy (i.e. X days or Y terabytes of storage consumed), or, of course, the relay shuts down.

But as far as I know, no standard approach yet exists, so we must assume at this early stage that our notes are ephemeral.