I posted this on the Mt Whitney Facebook group:
Lost and found hiker: Cautionary tale.
Mazzie VanRoy posted a thread here:
...that her friend was having trouble on the trail. He started at 11 PM, summit at noon, then darkness overtook him on the descent. The trail below Trail Camp is tough to follow in the dark--There is a switchback that can be missed, and bad decisions (to continue down Off-Trail!!) has been deadly before.

He lost the trail, but his InReach communicator was helpful in that Mazzie was able to tell him where the trail was in relation to his position. After being on the trail for 27 hours, he had to crash (get some sleep). He hit his SOS button, and shut down the gps unit. It appears that around 5:30 AM, he was up and heading down. Fortunately he found the trail, reached Whitney Portal about 36 hours after starting up.

Several Important points:
1. Set up a turn-around time. 13 hours to summit, with only 5 hours of daylight remaining is way beyond reasonable. The mountain will always be there, but that doesn't help if you don't make it back to the trailhead.

2. When hiking alone like that, having a two-way gps communicator (InReach) could save your life. The ability of Mazzie to tell him how far away he was from the trail might have saved his life.

3. This is for Mazzie: don't "blow up" the hiker's unit with messages. It requires a lot of messing around to stop, read extra messages, and then respond. Also, in canyons like that, satellite communications don't get through immediately -- it can take 15 minutes, sometimes longer, for a satellite to come into view above the hiker.

4. It is good he had enough warm clothing to survive the cold overnight. Hypothermia can cause muscles to fail, and it can also cause a dementia-like stupor, resulting in making fatal mistakes.

I am sure there are many more useful lessons from this story. Mazzie, thanks for sharing, and everyone is really glad he made it down safely.

By the way, for anyone reading this: The InReach has a valuable iPhone / android app: If you download the maps before heading out, you can find your position on the maps on the iPhone while you are out on the trail. It can impact the battery life on the phone unit, but I have found it extremely helpful, especially when off-trail.