What does Krakauer think happened to Hansen?

From the text:

On May 23, when David Breashears and Ed Viesturs reached the summit, they would find no sign of Hansen's body; they did, however, find an ice ax planted about fifty vertical feet above the South Summit, along a very exposed section of ridge where the fixed ropes came to an end. It's quite possible that Hall and/or Harris managed to get Hansen down the ropes to this point, only to have him lose his footing and fall 7,000 feet down the sheer Southwest Face, leaving his ice ax jammed into the ridge where he slipped. But this, too, is merely conjecture. What might have happened to Harris remains even harder to discern. Between Lopsang's testimony, Hall's radio calls, and the fact that another ice ax found on the South Summit was Positively identified as Andy's, we can be reasonably sure he was at the South Summit with Hall on the night of May 10. Beyond that, however, virtually nothing is known about how the young guide met his end.