A friend of mine and I rented a AWD vehicle to be able to drive on the "F roads" in the internal part of Iceland, which is beautiful but very desolate. (I'd be surprised if the inspiration for Mordor didn't come from some places Iceland in fact.) I had downloaded the OSM maps on my tablet and was just manually plotting routes that looked like they could be interesting.
It was great fun, but it sort of turns out that there are F roads and there are F roads. Some of the roads are fairly flat, easy to pick out, and you see a car at least once every hour. Some of the roads... well, one road went steeply up, then without warning into what was basically a giant sand bowl half a mile in diameter. We were in the "bowl", with sand who knows how deep (deep enough that the car had trouble making forward progress) before we knew what was happening. In the middle of nowhere, with no cell signal and not having seen anyone for hours.
Thankfully, by turning around and just keeping the accelerator on, we were able to build up enough momentum to get back over the ridge by which we'd come in; but it was definitely a close shave.
I could imagine the same story as TFA happening with OSM maps.
If such tags are present and seem to be reliable, then OSM can be used to plan trips. Otherwise it is just too risky to rely on OSM. In particular in harsh climates and if there is no way to get help.
I.e., before using OSM, assess the quality of the mapping done by the local community. Anyone can draw lines of a map by looking at satelite images. It doesn't mean that such lines are passable.
Taking a few minutes to zoom out and check the actual maps in terrain view would save most people on these journeys.
If you don't have data access then Google Maps routing won't help much either. It all comes down to offline/hard maps, situational awareness, and basic wayfinding to get through these areas safely.
EDIT: what are people disagreeing with here?
Streambed: https://www.google.com/maps/@34.991622,-108.0730561,94m/data...
Lightly used dirt roads: https://www.google.com/maps/@34.9927729,-108.076162,158m/dat...
As for the data issue, Google maps (by default?) caches the turn-by-turn directions when you start navigation. Spotty cell service isn't really a problem until you make a wrong turn.
Zoom out, assess the terrain, look for markings, check for buildings, and compare paths to the destination. Unless you're visiting the bottom of the crater there, you shouldn't ever be going off that main highway.
The map tiles should also cached (how else would it show you the turns?) but yes offline/paper maps are a must when going into unfamiliar areas.
That said I do think people should carry a $15 paper map booklet if they plan on venturing outside the city. I both have offline maps of the whole US and paper maps in my car, but I also do this a lot.