Unfortunately it is not possible. Having said that, we have had instances where a full email job grid has been deleted (unintentionally) and we have had to restore the detail from a backup. So, in essence it is possible, but we do charge for the time to both pull down the backup (this can take anywhere from between up to 5-12 hours) and then to patch the live database with what has been deleted.
If you have accidentally deleted an Email Job, it will mean that the links to any documents that may have been included in the email that was sent to a Client will no longer be active.
We would recommend that the email job be recreated.