Names and places changed to protect the guilty.
With around 100 hours on my PPL (with IMC) and a gliding silver C and - importantly some rotary wing time (where over-control kills you quickest) - I had the opportunity to sit right seat on an empty repositining flight in a bizjet in the Falcon 900/Gulfstream GV category. Just followed the flight director and took it down to 200' on the approach. Left seat said I had it set up nicely and could easily have landed it. Best fun you can have with your clothes on!
This a/c had a small fraction of the inertia of a 100 seat+ airliner, the flight plan was fully loaded into the fmc and I was not under any pressure, plus I had an instructor in the left seat doing all the work of configuring the a/c and talking to the ground.
My guess is that if everything was nicely set up and peace and calmness prevailed and the ppl had luck on his/her side and never deviated by more than a few feet from the ideal profile, then it might be a survivable touchdown - even if the roll-out killed all on board. How many of those factors are going to be in your favour when you have to step up to land a 737 with an incapacitated crew. You've already run out of luck before you sit down!
Interesting point about landing at the airfield. I wonder if you might be informed by ATC that the highest chance of survival would come from ditching just offshore - on the same principal that we are told that the safest thing to do following SEP engine failure at night is to head for the dark bits - your chance of survival virtually nil but at least you don't embarrass the CAA by killing people on the ground!
Good luck Aunty Mabel - but I hope you will understand I don't want anyone I know to be in the back when you get your shot at glory!