It seems that the man who felt responsible because he forgot the ladder and lied that he owned the boat, but didn't, couldn't cope with the guilt that all but one of the others had died and after managing to get the young Mum back on board, drifted away and didn't climb back on after she released the steps. She then jumped back in to save him, but the next morning when they showed the fishing boat circling them. it seemed he was lying dead on deck!
There is a similar film called Open Water about a young couple left behind after a scuba diving trip - equally harrowing and also based on a true story -have you seen that?