I would concur it would be best if you really need to do this to restore a complete database and if needed file backup too.
Trying to manually add them back via the database directly would partly work but you may run into some annoying and difficult to fix issues, not to mention their old data may not be 'owned' by them when they are restored.
Database is afaik relational so you cannot just usually get away with restoring their details in the appropriate table.