This is why everyone needs to do just a little research before they go. A simple search of climate for the area or looking at the NPS web sites will give the temperature ranges you will encounter.

My family has made fun of me in the past for my preparations for trips (not so much anymore - I think they've given up). Their thinking is "What kind of fool packs fire starting and signaling materials for a cross country trip, on the interstate?" We've never needed any of it. But I still make sure it's available every trip.

My thinking is that once you find yourself in a bad situation, you WILL make bad decisions. While we look at people like this family and say, "She shouldn't have left the car", and be perfectly correct in that assessment, I imagine things don't seem so crystal clear when you're actually stuck and worried about your kid. Hopefully, those potential bad decision times are when I would remember to pull out my fire starting, signalling, shelter, cooking, emergency medical, and other "stupid stuff" that I packed and turn things into an impromptu camping trip.

Because it is so ingrained into me to prepare in advance and not rely on emergency decisions in the heat of the moment, this makes me less understanding of people that head out blind and assume "we'll figure it out when it happens". Especially when you read so many news reports of people who went in clueless and came out dead. I can't fathom how people ignore that and continue on in complete ignorance. As I get older, I tend to get mad at them for their stupidity, which I really shouldn't. I'm more accepting of adults who meet their demise due to stupidity, but I'm not as forgiving when they drag their unknowing kids in with them.

Pre-trip planning would also have given them the info that the park was closed.
North Rim Road Conditions

It is not necessarily true that you WILL make bad decisions. Many people will, but it is avoidable and you can train to not make such bad decisions.

A little practice of the right skills will make them salient in your mind and become the default response.

A little thought about your plan, and what is the worst thing that can happen, will help in avoiding such situations and will make sure you think through how to deal with them.

As a Scout Master, along with my military time, means that I think through the plan, and the worst case, almost automatically. I can't help it, it is too ingrained. It does not need to frighten you, just make you think through what could happen and how you can handle it.

Along with the Wilderness Survival merit badge pamphlet I recommended before, get the Emergency Preparedness one and the First Aid one. I like teaching these merit badges close together in time, as they are all connected and mutually supporting. Emergency preparedness will walk them through weighing the possibilities and preparing for them in a practical and logical way. It is suitable for kids, but works for adults as well. They are inexpensive, and I recommend them over many survival books out there. They are also small and easy to have with you. Just the process of stopping and reading them when you find yourself in such a situation will help to calm you and focus your mind. Drink some water, eat a snack to feed the brain, and you will find yourself becoming more calm and rational. Then you camp out unexpectedly, and make it out without too much risk.

Pre-trip planning would also have given them the info that the North Rim was closed.
Park Road Conditions & Closures

The South Rim was open, but that's not where they were. It took all of three minutes to find out that this time of year you had better be going to the South Rim.

"Could have, should have" are all good in hindsight and easy for people on this forum to pick apart. The real bottom line is that unless the person(s) already have a ETS mindset, they are not going to be doing risk assessments nor looking on this forum or any other before they travel. Unfortunately it takes a life in balance survival event such as this before people maybe learn from their mistakes.

My experience is that the overwhelming majority of folks who get into trouble in the wild are naive/inexperienced/ and unaware of the potential hazards nor are they informed as to the most elementary measures useful in forestalling problems. People with even basic knowledge and skills are seldom the focus of SAR operations.

I am fairly sure that most, if not all of us, have blundered at some point in our past and learned therefrom. That is certainly true for me - I am one fortunate dude.

A bit of clarification is probably in order. When the NPS says the North Rim is "CLOSED", I think they mean that facilities are closed and roads are closed to vehicles. I don't believe they will bust you for simply going there, though they might ticket you for driving on a closed road. (hikermor or other please correct me if I'm wrong.)

In fact my understanding is that quite a few backcountry skiers visit the N Rim in winter. Case in point, some years back a friend of mine, a very fit and highly experienced backcountry traveler, skied in solo from where the road was closed to a N Rim trailhead, tied his skies to his pack and changed into hiking boots, and hiked down into the canyon and back up to the S Rim. My recollection is that he said the biggest problem was that the trails just below the rim were quite icy in spots and required careful walking. This is of course very different from inexperienced people driving down from Vegas, probably planning on taking a few selfies and then driving back to the casino.

I think the biggest thing these folks lacked was simple common sense. If the main road is closed for the winter, why in the world would any sane person think that a smaller forest road would be open?

According to the web site, the NR is essentially back county after December 1, when services, both concessionaire and NPS, are terminated. People can use the campground (no running water) and technically you need a back country permit. The roads are not plowed and the entrance station is not staffed. My understanding is that the road fro Jacobs Lake is not plowed at some point, which should be a clue to vehicle users.

I have not ski toured on the NR, but it would be sublime with the usual good snow cover. It really is beautiful country, with access to whole vast vistas of the Canyon which are essentially inaccessible to the South Rim hordes. My visits have been during the time when facilities were open.