Those of us who do fly over terrain not suitable to land on are well aware of the risk
Height is your friend on this one, I have crossed the great divide many a time and probably the longest time I would have is 5 minutes max when no options are available forward, back and off to the sides, at all other times I remains within gliding distance of grassed valleys / cleared areas and high country roads
But I take this as a minimal risk as usually the engine has been performing perfectly for 35 minutes before getting to no mans land and if it is going to fail in that 5 minute period well I'm just Sh!t out of luck then
I would never dare fly over the divide at tree top level or even a 1000 or 2 foot above it, most times I'm 4 1/2 or more above it
Every time we fly we take a risk, every day we drive we take a risk, actually every day we wake up to tackle the day ahead is a risk of something happening
Minimising the risk goes a long way in every way