I watched this episode as well. The one thing that does point to Ben being in the cave was that the final diver, the woman from Australia, did find what is believed to be Ben's shovel way back further into the caves than any of the other divers had gone. I think she was smaller and was able to go further. She also said that there is a slight possibility he could be stuck in a crevice, as divers can panic and try to crawl into small spaces when running out of air, i.e. Personally, I do think he is in there, one way or another.
It was never explained why he was carrying over $1000 cash, which was in his truck. That seems like an awful lot of cash to leave in your wallet for a day of diving, but may be unrelated.
What security footage was available showed nothing unusual for the day he vanished.
It was kind of disturbing to learn that he was not certified for cave-diving, yet had found a way to undo the "gate" to the caves underwater, since he could not get a key. Yet the day he disappeared, the employee did give him a key or let him in, as he said that Ben would have been in more danger the way he was getting in on his own, by going under the bars or something.
It is very strange that he has not been found, but since no one has been able to get to the end of the tunnel, I guess it is possible he is there. If someone was determined enough...plus three of his tanks were found, so if he shed those, he would not have taken up so much space.
He HAD been thru depression over the death of his brother and the huge financial issues he had suffered and was still dealing with, although his family feels certain that he was not suicidal.
In any event, a very sad mystery.