All possible hypothetical scenarios where a non pilot has to land a big jet assume that he can talk to someone who can tell him what switches to press, what headings to fly and what speeds etc.
So, the first step is to find someone to talk to. Ah! First problem. Which one is the Press to Transmit button? How many non pilots (or even PPLs) could find the P to T button first time? i.e. without first accidentally switching off the autopilot, at FL350 and Mach.7? Phew! How many PPLs could hand fly a B737 at that speed and live, let alone a non pilot? I wouldn't know because I've never done it.
I have landed a BA B777 simulator 5 out of 5 times (once at Jersey) but I still wouldn't rate my chances of doing it live for real. But I never had to find the P to T switch.