I saw a version of the "rescue sub" which was a type of long bag that looked like a body bag you would use for a corpse. It was to be tief to a rope and pulled along. I've been in caves and their walls are not smooth. I've hit my head on their low head-space. That craft would have snagged and it is unpredictable if would have held together.
Below is the actual craft. Because of its length and rigid construction, I would expect a dry run to see if it would go through those tight passages. Did they have the time for such a test?