The positive load factor in a Ac500 is around 4.4g, the negative 2.7g.
If your buddies in CW ever got anywhere near -2.7g, I would be very surprised.
What you may have experienced is hard nose-down at the top of a climb. In the order of zero to -1g.
Don't know what could have caused loss of power on an engine, perhaps fuel starvation.
Normally aspirated engines lose power very easily due to the carb float moving to the cutoff position.
The accident in Tassie was likely to be possibly caused by autopilot down-trim runaway, taking the hapless pilot through VNE very quickly.