If you turn off Touch ID, it appears that iOS will still keep your fingerprints in the secure enclave. If you reenable Touch ID, iOS will ask if you want to reinstate your old fingerprints. This is a good timesaver, especially if you added multiple fingers, as you won’t have to go through the Touch ID setup anymore.
In order to ensure they’re your fingerprints, you’ll have to enter your passcode, presumably the one set when they were added to the device.
