Touch ID does not work after a reboot, to many attempts or a long of delay.

Additionally you don't have to use your thumb, so if you don't know what body part was used your out of luck.

If the phone is rebooted or if 48 hours have passed since the last passcode was entered, the touch ID can't be used to unlock the phone.

Touch ID requires the passcode after reboot or timeout. They'd need to do it very quickly.