you can play the what-if's all day long, but at the end of the day, In Illinois anyway, you are arrested, charged, and convicted if you are found intoxicated in the drivers seat of a motor vehicle, even if parked, especially if you have the vehicle running.
I am a police officer that works in a very rural county. I can honestly say I would say a 40% of the adult population are alcoholics (and I am being conservative). And do not mistake me for a guy that believes everyone that drinks is an alcoholic, as I drink as well. work in a very rural county. Here is how I handle the situation. If I get called to or find a person passed out in the drivers seat of a car, I will offer them a ride home. If they take it, I give it to them, If they don't, off to jail they go.
I could not in good conscience leave a person passed out drunk in an automobile. What if that person I left there woke up 5 minutes after I left and decided to drive home?