If you check the CAA website you will see that the minimum requirement for a heli to run IFR includes twin engines, stablisation, etc - you can't get single engine IFR helicopter. So even with one engine out at 500ft, you still have power - usually enough to continue to fly, though often not enough to hover. Hnce you would vacate on one engine, divert to an aerodrome and erform a run-on landing.
Not a big issue, really.