The suggestion sounds good at first glance, the problem is that the driver doesn't spend all day turning left where cyclists or pedestrians might be. Having a passenger is a distraction that could cause other incidents to occur. It's like talking on the phone or listening to the radio.
Not only that, but when the designated person forgets is their responsibility and someone dies as a result, yes there is someone to blame, but it still doesn't help the dead person.
Personally I believe of you take the responsibility away from the driver, the situation would be worse, nor better.
It isn't like talking on the phone, acksherly - there have been studies on the effects on driver concentration of different kinds of possible distraction. And the thing about forgetting is addressed by changing the work culture and obliging people to take responsibility. At the moment nothing much happens to drivers who kill people, or to the companies on whose behalf they are killing, because it isn't seen as their responsibility. If you oblige them to take responsibility and face the consequences, they will stop doing it, and your hypothetical dead person won't need helping, because she'll still be alive. Safety on construction sites has improved beyond measure because it is now taken seriously - presumably whatever you mean by "human nature" doesn't apply there...