interesting since I believe in EASA-land a HEMS aircraft must have that capability for live winching which is why air ambulances with winches aren't a player in UK.
Not true:
JAR-OPS 3.005(h)(d)(1)
The Helicopter. During HHO, the helicopter must be capable of sustaining a critical power unit failure with the remaining engine(s) at the appropriate power setting, without hazard to the suspended person(s)/cargo, third parties, or property (Except for HEMS HHO at a HEMS operating site where the requirement need not be applied.)
EASA SPA.HHO.125 Performance requirements for HHO
Except for HHO at a HEMS operating site, HHO shall be capable of sustaining a critical engine failure with the remaining engine(s) at the appropriate power setting without hazard to the suspended person(s), cargo, third parties or property.
Training has to be conducted with OEI Performance (just like SAR)