How about an engine failure in full IMC in a Chieftain / Nav close to MTOW and unable to maintain altitude. But how to deal with that, I have no idea. That happened to someone a while back but I don't think it was in IMC.
Another guy in Chieftain a while back loses all electrics at night from Tassie to Essendon, no radios, torch only, over Bass Strait in IMC with no visible horizon (obviously). Not life threatning, but scary none the less.