On July 4, 2012, Paul Michael LeMaitre disappeared during the running of the Mount Marathon in Seward, Alaska. The race trail is about 3.1-3.5 miles, and the elevation of the mountain is 3022 feet. LeMaitre was last seen about 200 feet from the top. His body has never been found despite extensive searches. This was during a race that had something like 800 entrants. If someone can disappear during those circumstances, it is not a stretch of the imagination to believe that someone hiking alone in at higher elevations could disappear as well. I don't think foul play was involved.