Let's look at this objectively.
I would think by "fault" you simply meant a causal relationship rather than a "moral" lapse.
So, who's fault?
Yours? No, you attempted your best to inform him.
The Cliff's? Nope. The cliff was simply doing what it does best.
The shoe company which manufactured the shoes he was wearing? Nope.
In other words, the "cause" of the man's fall was none other than his own. He was deaf and blind. If he didn't know where he was, the last thing he should have done was to walk aimlessly around. If he knew where he was, he should have known better than to walk over the cliff.
Perhaps he did it intentionally?
But the facts remain. That man freely chose to move his legs in such a way that he walked over the cliff.
There were many options he had. He could have used one of those little stick thingys that blind people use. He could have simply sat and cried out for help.
But, for some reason, he thought he knew better, so he decided to go walking.
Jean