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...So yeah, it is totally technically possible to rip the TouchID sensor out of your phone and still be able to unlock it (assuming you have the passcode). TouchID is not essential to unlock the device; it is only ever a shortcut for entering the passwords you have already recently entered in to the phone.
Law firms? I just did all of your investigation work for you. Feel free to cut me a cheque.
Nice long explanation. I missed the part where if I used a "third party" home button without TouchID, I would conceivably compromise security even though I needed to enter in a passcode in order to use the phone in the first place after power-up.
I will repeat what another poster said, the passcode is the primary means of getting in to the phone and is required just to enable the TouchID/A7 processor "handshake" (as I understand it). When enabled, the TouchID and fingerprint scanner is just an alternative but convenient way to engage in sensitive transactions without re-entering the passcode; An option many iPhone users do not even use. So why "brick" the phone in the name of security when a "passcode" is always required at power-up just to use the device ??????