Some years ago, before I got my PPL, I had an hour in the 747-400 simulator at Cranebank. It was what convinced me to do the PPL.
We had a lengthy brief prior to going on board and firing the sim up. The Instructor then set me up on a 15 mile curved approach to one of the runways at JFK. He talked me through it but his hands remained clear of the controls at all times. His only proviso was that if it looked unsafe he would take control (it taking a considerable time to reboot the sim if I "crashed" it). Coming out of the curved approach onto the glideslope near the outer marker he asked me how it looked - I said "it looks about right". He said "looks good to me - go for it." Amazingly I greased it on and brought it to a full stop, much to the amazement of the instructor. We taxied the big beasty round straight into a rolling take-off, followed by circuits and bumps. The instructor did clean things up for me after each take-off, but then on downwind he talked me through the landing set up. Each time greased on, though the final landing to stop was a floater landing long but stopped well short of the end. The Instructor then did a 10 minute guided tour of the New York skyline at 500' - impressive, followed by a short-field landing. By the end of the hour I was a complete wet rag, dripping in sweat and the high level of concentration beginning to tell. In the debrief the instructor did ask me whether I had ever given thought to becoming a pilot - well the rest is history as they say.
In the real world with crew incapacitated I personally would rather have a PPL have a go at the landing than no one at all. I think it probably raises chances of survivability to about 50/50.
The real difficiency of the sim-experience is that the instructor sets things up for you - usually a take-off or landing. It might be an interesting scenario to take over a sim on auto-pilot in the cruise and try to bring it to land with instructions only.