From [Lemmy documentation](https://join-lemmy.org/docs/en/federation/overview.html#revert-a-previous-action):
> We don't delete anything from our database, just hide it from users. Deleted or removed Communities/Posts/Comments have a "restore" button.
But don't take my word for it. Try it out yourself. You can make a comment, delete the comment (your username appears to remain) and then restore its content.
Not from a privacy perspective, that’s for sure. There are already a couple privacy downsides in federated services in general, but the decision to intentionally retain user data after deletion is requested… If that’s the case, Reddit may offer more privacy