Hindsight is 20-20. I suppose there are several items that could have made their situation less dire ... satellite phone, emergency beacon, cold-weather gear, food and water, and more. Certainly driving through winter-weather areas call for emergency supplies packed in the trunk. Most of us in the north do that as a routine matter (or at least we all know we should).
Fact is, this couple seems to have done alright, surviving 6 days while snowbound in their vehicle. Don't know how much longer they could have gone, but they did make it out alive because of the selflessness of the searcher who located them.
If there is a lesson here I would draw, it would be the need to pay attention in unfamiliar areas. They missed the signs that could have prevented their ordeal. Who knows why that happened? ... probably distracted by something or other. Inattentiveness in any situation greatly increases the chance of trouble rearing its head.