If you are running time machine :
Set the focus of Time Machine to Mail.app and you can traverse back and recover your mail.
If not, you may need to take the machien to a specialist and have them run specific data recovery tools on them to try to rebuild the data from the drive.
If you can, the proper way is to recover them through backup (time machine)
If they are not there and If you are lucky you may be able to rename AddressBook.data.previous to AddressBook.data and recover your contacts.
Be sure to back up before you do this, so you do not break anything further.
You may have to quit Address Book (after backing up) and reload after renaming for the old data to be loaded.
It could help you retrieve deleted data.