Matspart3
100% or engines failures where the engine wouldn't start again were found to be in this category
Seriously, I don't think you could assemble a homogenous enough sample for the probability to be too meaningful.
Night SEP flying is very safe unless you are one of the very small number of people who has a big problem - I remember a C172 going into the Forth in darkness a few years ago, can't think of one in the news since.
So if you play the probability game, it's likely to be small, but the impact is potentially very severe - so what is the total systemic risk? Most likely a matter of opinion.
Classic risk management offers 4 options - (a) avoidance (b) mitigation (c) acceptance and (d) transference to a 3rd party.
Assuming that (d) is not viable here, you can choose not to fly at night (a), fly near the airfield as I do or some other action (b) or (c) take the view that it won't happen to you - looking at the small instance of incidents this is a serious option.
I haven't got the numbers to hand, but I read a report last year that asserted that GA flying is much more hazardous than driving per se and demonstrated that it is airline ops which are mcuh safer.
Cheers
F3G