Photo Streams on iCloud are intended to be a syncing service not a backup. My Photo Stream is restricted to a 30 day 1000 photo limit. If you delete the photos from Photo Stream they will be removed from the server as well. If you just turned off Photo Stream re-enabling it will return only the photos still on the server.
Photos in the iPad's Camera Roll are stored in the backup file as long as you have not updated the backup after deleting the photos. To recover these photos you will have to Restore the iPad using the backup.