Helicopters are unique in that it’s airframe has no life expectancy associated with it. If the airframe is well taken care of it can last indefinitely. The airframe of a helicopter makes up only a small percentage of the overall value. The components of a helicopter are very different than that of an airplane and consists of a tail rotor gearbox to drive the tail rotor, an engine (or two) that drives the main rotor drive system (main rotor gearbox), mast, and main rotor hub and blades.
There are many parts on a helicopter that are considered on condition. This means that as long as these parts are inspected at the required intervals and found to be in an airworthy condition there is no life expectancy on them. Conversely there are parts/components on a helicopter that are life limited and must be retired and replaced in relationship to when the OEM states the component life ends.
In relation to the major components, (engines, gearboxes, etc.) their overhaul times will come due at different times and overall value of the helicopter will vary depending on how much time is left before overhaul of each component. The same holds true for life limited parts. Helicopters tend to hold their value very well. It is important to find someone with a background in helicopters when looking for a value for your helicopter due to their unique qualities.
