It seems like Lemmy will delete all your data once you deleted your account. It sounds to me like Lemmy will remove all the post and comments as well.
However, I think some of the posts and comments might be helpful for others, all I want from deleting account is to remove my username, so that others cannot piece together my comments and posts.
Is there a “deactivate” option like reddit where it only remove your username from the post, but not the post?
Lemmy isn’t very precious about you having multiple accounts. What would the advantages of deleting the count be over changing the username? Except, I suppose the risk of a compromised password reviving it.
Don’t count on deleting/modifying to work at all with federation. The data is send to and stored on other servers in the federation. (In fact, Lemmy by default only soft-deletes, so any server admin can recover deleted information from the database.)