Okay adding a slightly different twist - you (you being a qualified PPL) take a friend flying in your Cessna/Piper, your friend has never flown or been in one of these planes before – you go unserviceable so to speak - do you think your friend could land the plane at an airfield?
My guess is if they can find the transmit button - then maybe - if they are very lucky...
GrasStrip, this has in fact happened several times,
HOWEVER,
AFAIK only with people who had at least some exposure to an airplane environment. A PPL in the cockpit of a 747 would have that. Doesn't mean he/she could land the a/c. I guess the biggest danger, as
Floppy Link has pointed out, would be the inadvertent AP disconnect. Once past that, well, perhaps. Would love to try it in a sim (have landed jets in sims, but nothing near as heavy/complex), but most certainly
NOT in the real world !!