Deleted message at backend

Just activated the plugin and set everything up. After some testing on deleted message by an user from the frontend, my conclusion was if the message is exchanged between 2 users, and if the message is deleted by 1 of them, the original message and all its replies will still remain at backend unless the 2nd user also delete it. Is this conclusion correct?

IF it is correct, after both users deleted the message and the entire thread disappears from the backend, are they gone forever?

I’m hoping to keep deleted message at backend for some time before let them go forever? Will that be possible?

Thank you.