As I said Special 25 I do not have the graphs so that is just a guess but from memory it is not far off. I was only answering SASless's Q about hover weights anyhow. There was no reason in this instance for the crew to calculate that.
They would have calculated the DSELW though and if their AUW was higher than that then there would have been no option to land on the helideck. That limits options to flying back to the beach on a single engine (if that was the problem) or ditching. Crews decision - unless it was made for them by another problem.