Maybe the best you can do here is to contact the rangers or SAR as soon as possible and report a disoriented hiker who refused to abandon their hike.
Given the lack of cell coverage on Whitney, what would be the best way to call for help?
A friend who day-hiked Whitney in mid-July (let's call him Mark) turned back near the JMT junction due to exhaustion and AMS. Mark took a long time to get down, but on his way down, he passed a guy in his 60s who looked to be even worse off than him. This happened near Trailside Meadows, and the older guy asked Mark whether he could borrow his phone "so that he could call someone". Mark took out his phone, turned off airplane mode, and lent it to him, but there was no reception at all in that area.
After several failed attempts, Mark took back his phone and continued heading down. He thought he heard the older guy mumble something to the effect of "I hope I make it down by night" (this incident occurred at around 1 PM) but wasn't completely sure. A few minutes later, Mark looked back and saw that the older guy had barely made any progress in going down.
Mark told me that he felt really bad but didn't know what else he could do. He was already running low on food himself and couldn't afford to give anyone his snack, and the older guy said that he had a filter and enough water. The only ranger Mark saw on the trail that day was checking permits on the switchbacks shortly before noon, and he had no idea where that ranger had gone since then. He considered alerting someone at the Portal when he got back a few hours later, but ended up not doing so since he thought that other hikers would already have helped that guy out.
