You can check the road surface, see the surrounding terrain, check for any signs or intersections or proximity to structures, etc. At the very least, you should zoom out enough to check that your path actually ends up going to your destination.
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.
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.
Like I said, if you zoom out then you can clearly see the actual "Ice Caves" road #53 with lane markings, and a smaller "Ice Cave" dirt road that ends near that group of buildings. Everything after that is just dirt, no roads at all regardless of what Google says, which is my point.
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.
The area is actually full of ice caves and native sites that Google will send you on those dirt roads to get to. Also, regardless of what preparations people ought to do, there's going to people who rely solely on one method without backups. It should be robust to that.
I’ve been on legit roads in the middle of nowhere and not seeing marking or roads doesn’t mean anything (western USA problems).
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.
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?