mechanical failure accounts for less than 15% of fatal IFR accidents. Of those, about half of them will be vacuum and electric system failures, a quarter fuel exhaustion and a quarter mechanical engine failures
So, 1/4 of 15% i.e. 4% of fatal IFR accidents is engine failure.
That's not bad - I am not planning to run out of juice, an electrical failure is covered by having a vacuum horizon and a decent handheld GPS plus a handheld radio, a vac failure is covered by having an electric horizon+TC (plus staying awake). All these are arguably pilot errors - running out of juice definitely is.
So the risks due to engine failure are very low.
-