Of course it is all based on probabilities etc, CASA is all about risk assessment and deciding what is an 'acceptable' level of safety. Why does your friend fly at all? After all it is a statistical certainty that at some point a passenger aircraft will crash and kill everyone on board, it has happened before and it will happen again so the only way to keep flying safe is for CASA to stop allowing aircraft to fly? How may all engine flameouts have there been, I can think of two off the top of my head:
1 - BA 747, all four out due to volcanic ASH
2 - A320, both out due to bird ingestion.
So on the basis of that it makes no difference if it is a 2 or 4 engine aircraft :-)