Can you clarify a bit about what you are trying to achieve?
Do you want all the user data except for posts to be deleted, and posts to be only soft-deleted (kept in the database, not visible publicly)?
I believe if you delete a user, all the posts are soft-deleted. I tried on my test instance:
I don’t know if they are cleaned up after a while, and I believe attachments will be removed after some time.
I’d need confirmation on this. 