as above
The landing velocity after engine failure will be limited by the U/C design criteria, an aircraft designed for shipborne operations will be allowed to land with a higher velocity than a pure civil type. Wheels or skids are another factor.
Minimum rotor speed may be determined by considerations such a head stresses, controllability, tail rotor authority or electrical generator rotational limits and will vary aircraft to aircraft
Remember that HV curves also apply to flyaways so a succesful landing may be after a flyaway and circuit.