When I ran my group through the first time only one survived. It was a very intense adventure for them. Especialy at the end were every roll they made seemed to be life or death. I really looked at the numbers the second time and I noticed this as well. I did the same sort of thing to solve the problem. The lone survivor wanted to dive down and bring everyone up for resurection. I wanted to make sure the depth was right and make sure things weren't to easy. I was probably worried over nothing. No one was the wiser the second time down.