From the responses to this post I'm concluding that all notes published to nostr will eventually disappear.
Not a critisism, just an assumption.
Discussion
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.