I'd disagree, but only in hindsight, that they BOTH might have made it out if he hadn't cut it. They BOTH would have fallen to the same place joe did with the broken leg, and sure, maybe they'd both have bad legs, but the chances of survival are better with two than one. And that joker in the tent might have had the wherewithall to get help if neither of them came back. And the reason joe kept going was that he didn't want to die alone, which is something none of us want to do.
What was the name of the english band that kept coming back to him with that song that he couldn't get out of his head?