My assumptions
I have 5 relays chosen.
Notes I create are sent to those relays.
In future all those relays close down.
Are all the notes I sent to those relays lost?
Discussion
Think that's correct, but Nostragram & Iris already allow backups. Nostragram seemed to allow download or broadcast to specific relay.
It should be pretty easy for clients to store its own events as a backup. Could even be done as a default. In the situation where your relays go offline, you just transfer all your events to a new relay.
Run your own private relay that only you can write too.
From the responses to this post I'm concluding that all notes published to nostr will eventually disappear.
Not a critisism, just an assumption.
All tweets posted to Twitter will at some point disappear.
Quite quickly in some cases.
I don't think it's a useful assumption.
Know that Bitcoiners like to keep the receipts.
I downloaded all my 8000 nostr events in a 2mb file.
It's safer to assume that they'll exist for as long as nostr exists. It makes you become a little more careful with your words.
Technically I think (could be wrong) clients could send events (eg notes) that they haven’t directly created to other relays.
So if you post a note to relay X, my app downloads the note. It is then possible for my app to post the note to relay Y… thereby propagating it throughout the network of relays.
In practice I don’t think this is happening but rather the list of relays containing the note is instead propagated (NIP-65)
That's my understanding too. All prior events are signed and can therefore be sent to a relay by a client for distributing.
I think the line between clients & relays will blur over time.
There are many reasons why you'd want to have them both running on the same machine.