The order was the same for both Joe and Janet but I think the sponsors' intentions were different for each: Joe was a priest so he shouldn't have killed anyone but he did. Janet is a mother who is worried about her daughter so maybe the odds were that she was going to kill Joe. In that sense, I feel Janet, like Joe before, passed the test. For proof of that, the "Sponsors" continued to test her, sending a cab for her and Joe.
(I still keep on the back-burner, the possibility that this whole charade is about betting on individual's reaction. The "message in a fortune cookie" would fit in well here. There's no greater good, that's just incentive for the game pieces. It's only about bored billionaires having a little fun.)
Or maybe neither Joe or Janet could fail the test: Whatever action they took would determine their place in the organization. If Janet had killed Joe, she'd be the new Joe.
"So did someone want Joe dead and provided a very convenient -- not to mention ironic -- method of demise? If so, what was the backup plan? What's happened since that they've decided the only thing to do is reprogram him -- effectively a sort of welcome back into the fold, or (from the previews) just sending out their executioner?"
Good questions. We'd need to know what happened to him between the time he was designated "best candidate in years" to his return to town. Did he fulfill his missions or did he fail? The exchange between Tom and Joe as they watched the new cargo coming in was pleasant enough. Since there was a long time between the "kill Joe" order and the reprogramming, I think it was simply another mission for Joe. Falling in love was the problem that forced reprogramming.