Single v twin...again? Don't make it military either, from records Hurricanes and Spitfires had only the one donk - and yes I realise they're not helicopters. Single engine Hueys in Vietnam? The Afghan war highlighted lots of issues, especially DA. Even an old RN colleague had an engine failure in a Lynx resulting in n emergency landing in Greece, not enough power to get into a hover back to the ship....at sea level!
Twin engines really should be for niche markets, the money saved by the odds of an engine failure make it more than worth it. We all seem to be happy for one engine during training,