Once Simon lowered Joe off that precipice, there was no other choice. He couldn't pull Joe up. Joe couldn't pull himself up. There was nothing solid to anchor Joe to, and Simon's snow seat kept breaking down in the soft powder, jerking him toward the precipice. Had Simon been able to hold on to Joe through the night, he still would have been hard-pressed to get him over to the place where he was able to come down the next morning.
You could also probably make a case that spending the night in the relatively sheltered crevasse was better for Joe than spending it dangling out in the wind and snow.
I agree. One last question though. IIRC, when Simon made it to Camp he wasn't alone, there were one or two other people there. I don't remember anyone trying to organize a rescue effort for Joe. Is that correct, or did they but were impeded by weather? Also, wasn't mention made by these climbers that they prided themselves on climbing with minimal gear, and would more gear have made any difference?