He very well could return it to Fed-Ex and say it is llegal for him to recieve, but this would not dissolve his involvement with the ATF, they will still want a statement as to what happened. Either way, he is going to get involved with them.
Shipping an item back he knows was illegal for him to ship makes him guilty of knowingly and wilfully commiting a crime, this would be as bad a decision as retaining possesion.
The best two decisions would be to either call the ATF directly, and throw the FFL under the bus and let him dig himself out, or best of all, let the FFL know and let him get ahead of the game and call the ATF along with you for a proper resolution. Now the FFL is raising his hand saying he got the shipping info wrong and the recipient isn't making the problem worse.
Now, let's look at a couple of other 'hypotheticals'. One from the recipients end and one from the FFL's end.
Let's say the recipient calls the FFL and says, hey you screwed up, want me to send this back to you so we can get it right? , but only after they contacted the ATF and they are trying to entrap him? Hmmmm, tinfoil hat time, maybe,but I wouldn't take that chance, I'd rather take my medicine legitimately and contact the ATF myself. At this instance, the FFL goofed up and the recipient has not commitied a crime.
Now, let's go at it another way. The FFL breathes a sigh of relief, accepts the rifle back, sends it to the proper FFL and the buyer gets it back. Next year, the ATF does some digging during a routine check, or maybe a check on the FFL since he has a propensity for screwing up. They find shipping records that trace back to this transaction and to what has happened. They go to the recipient and ask why he shipped the gun back to the FFL and he basically admits he was an accomplis in a felony.
I'm a poor gambler, so I normally only bet on the lowest risk I can work out in my head. I'm also not a lucky gambler, so I don't count on luck. To me the lowest risk is to try to correct a mistake than to defend a crime.
Is my thinking stinking? Enlighten me a little bit.