Some sort of flameout can't be ruled out, but it seems far less likely than a simple failure to push the power levers up.
He was at about the altitude where ice would have started to come off the airplane, which is where a flameout can take place, but I find it unlikely that a flameout (probably of only one engine) would have resulted in the vertical profile that resulted. More likely, a flameout would have brought his attention back to the power levers, he would have pushed them forward, and flown away and landed on one engine.
It sounds dumb that someone might simply fail to push the power levers forward after a level-off, but as an instructor I've seen it and (confession time) as a pilot I have done it when distracted. Ice makes it much less likely that he would have heard a stall horn before the stall.
The S-Tec 3100 has a nice airspeed awareness feature which will verbally announce "airspeed" and if the autopilot is engaged, will push the nose down at the same time. That speed is increased when the prop heat is on, to account for higher stall speed with ice on the airplane. I'd like to know if this airplane had a 3100, because if it had he might still be alive today, with nothing more than a scary story to tell over a beer.
