If anyone is interested, I was on this trip and it was me who made the decision to split the group and leave three people underground.
Given the situation I think I made the right choice, but I would be very happy to recieve any constructive criticism.
I'll try to sum up what happened and why I did what I did.
I had never done the trip before, but regard myself to be fairly competant and couldn't see any issues personaly with the trip other than the navigation. One of the group (probably the least fit of us) had done the trip previously without any dificulty, so I assumed that everyone would be ok from a fitness/ competance point of view. As one of the group had been through before and seemed to remember it well, I left the navigation up to him.
We were in no real hurry, we stopped to take photo's and generaly spent a bit of time enjoying our surroundings.
When we reached a large incline (with rails and winding gear on it) it became apparent that the chap who knew the way didn't know the way as well as he had imagined. He was however absolutely convinced that we were very close to the exit. We spent a considerable amount of time searching up and down the various inclines looking for the way out, switching off our lights in each one to look for any outside light.
This could have gone on for hours with no more success so I decided it was best to turn back and retrace our footsteps, at least this way we knew exactly where we were going and had a rough idea of how long it would take. Unfortunately by this time, two of the group were exhausted and didn't feel up to making the return trip.
The last thing I wanted was to end up with two people unable to move, to haul across a couple of lakes and up two pitches.
There were three other people staying with us in the area (from our club) one of whom had done the trip several times and definitely knew both entrances. My plan was to contact him, and he could come in from the Rhosydd side and meet the others and show them the way out.
We left three at the incline (we knew exactly where they were that way) and two of us headed out.
The three from the hut drove up the hill to the Croesor entrance, but with the weather (it was dark and foggy) they decided it would be unsafe for them to cross the hill to find the Rhosydd entrance, so we were left with no choice but to call rescue.
I went back in with the rescue team and we quickly found the others, where I'd left them, a little cold, but otherwise ok.
On a slightly brighter note, while we were down there, we pulled all but one of the dead boats out of the big lake, and took a couple out of the mine. The rest are out of the water in the passage on the Rhosydd side. 🙂
The distance between stupidity and genius is measured only by success.