The photos will not be deleted from the iPad if you turn it off on the touch. The photos sent to Photo Stream on each device will only be the latest photos taken after Photo Stream is enabled on the device. So if you turn off Photo Stream on the touch the photos will delete from it. Turning it back on will not add the photos back to it again, only the new photos taken on your devices will show up in the stream.
You can setup a Shared Photo Stream to copy older photos from one device to another. Ultimately you should be saving your photos to a computer with a proper backup program in place. Once photos are properly backed up and organized on the computer you can sync them to your devices with iTunes.