To the best of my knowledge, there have been no unplanned descents due to the failure of Amsteel or properly tied knots.
FWIW, I fish for big catfish with this stuff (65# PowerPro), using a Palomar knot exclusively. The only failure I've experienced has been when I've been hung up on something, and had no choice but to break off. It's not an easy thing to do.
The offshore boys that really push their tackle to the limits use knots with lots and lots of turns and wraps.