When I left for the second drive, the car's navigation app estimated I'd have 13% left when I arrived, and the estimates have been impressively good so I just went for it.
But I also was in a good sized metro area with a couple Tesla superchargers not far off my route, so my backup plan was to stop at one for 15 minutes if it ever looked like I might not make it.
20km is less than what he has left of charge. If the detour is earlier in the drive. He could have gone to a supercharger. If he gets stuck in a jam for hours, it makes no difference. The car hardly uses any power when standing still, it will heat the cabin but other than that it uses no power. I've tried this myself, I once got stuck in double digit cold for around an hour in a model 3 outside Hamar. It made no difference to my range.
But I also was in a good sized metro area with a couple Tesla superchargers not far off my route, so my backup plan was to stop at one for 15 minutes if it ever looked like I might not make it.