A mate just sent me these pix from North Qld.
The bloke who owns this boat was approaching Mackay harbour entrance at around 35 kts. He pulled back the throttles, but only one came off with a result it veered straight up onto the rocks. At high tide they pulled it off and took it inside the harbour wall where it now rests comfortably on the bottom, underwater.
That has to be the second good reason that I have heard for not having twin motors. (Not that I know anything about such things.)