The approach taken by Mercedes and others, including Hyundai, seems very lawyer driven. The worry is that a person falls asleep or passes out or just becomes inattentive. In any of those cases, disabling driver assist is the wrong thing to do and could actually lead to an accident. I propose a visual warning if no car controls have been touched for some period of time (90 seconds?). Note that tuning the radio or turning on the seat heaters or just tapping the screen all count. It means the driver is awake. If there is no interaction for a period of time an alert is flashed. Just touching the steering wheel will clear it. If it isn't cleared then there is a flashing alert followed quickly by an audible warning; all in quick succession. The next step is to assume the driver is incapacitated. The car turns on the emergency flashers and notifies Tesla who then notify the authorities. While this is happening the car waits for a straight stretch of road (where it hasn't been turning the car) and comes to a stop.
Compare the above proposed action to Mercedes. The driver has check pain and grabs his chest and then passes out. The car releases driver assist. It swerves into oncoming traffic and crashes. At least that is how I understand the Mercedes system from the videos.