There have been times when I've misjudged my level of tiredness. Drifting out of lane is a good marker that you've screwed up and need to pull over immediately and sleep.
Does Tesla have some way to determine wakefulness or to safely pull over if the driver fails to respond?
I'm sure the press is going to sensationalize the first accident caused by the auto-pilot, but seeing as it doesn't get tired or drink I bet the accident rate will be far lower then human drivers.
Not sure about Tesla but the technology DOES exist and some cars do currently have it.
You can then wake up the driver by actuating the seat or sounding an alarm.
The car will audibly, visually and via haptic feedback through the steering wheel alert a driver if the vehicle detects they are getting drowsy. Nothing new here.
Then there are all the jokes about using a http://en.wikipedia.org/wiki/Drinking_bird in situations like that. And then there's https://www.youtube.com/watch?v=Kv9JYqhFV-M to hack the Mercedes ALA.
Not exactly optimal, but I feel it may be the safest route. It would be interesting to see what other strategies people come up with.
EDIT: I have seen cars stopped on shoulders all the time. It may be dangerous compared to a parking lot, but this is an emergency situation. The driver is incapacitated and may need medical attention. I'll add that it should do more then run the hazard lights, it should dial 911. To keep driving means the car will run unattended for 200+ miles until the battery runs out.