It isn't long ago that the only EMS aircraft in UK were unstabilised, single engined RAF and Navy SAR machines, i.e. the Whirlwind. No-one complained about that. That aircraft had a very good safety record and it certainly saved many more lives than it lost.
When the Wessex was later introduced it wasn't advertised that it was safer because it had two engines; what was emphasised was that it was a more capable aircraft, mainly in range and payload.
Engine failures don't worry most pilots as much as tail rotor failures (myself included) yet there is no requirement for a back-up system on a tail rotor driveshaft on any helicopter that I can recall.
ShyT