Again, complete speculation on my part, and I might be totally wrong. But that last 3/4 of a mile is not at all easy, and there's little chance someone that thinks they're having a heart attack is going to walk steeply uphill, no matter how short the requisite distance. It's just not possible. My guess is, weighing their options, they decided to start in the downward direction, thinking that was their best chance at survival with temps dropping and night coming. They kept putting one foot in front of the the other, not necessarily planning to hike the whole 4 miles down. But eventually they found themselves at the trailhead. They should have informed their would-be rescuers. No question. But again they might not have wanted to call off the rescue, thinking any step might be their last. I suspect it was quite comforting to think help was on its way. It's also possible they lost cell coverage some ways down the trail, I really don't know. Lots of speculation on my part. Don't quote me on any of it! Unless I turn out to be right. ;-)