The COM client is responsible for managing the reference count on each COM interface it obtains on a NGWS object, just as it is on any other COM object. On the unmanaged side, the NGWS object is unavailable as soon as its reference count goes to zero, just like any other COM object. As far as the COM client is concerned, the object has been destroyed as it should be.
The only perceptible difference is that if the NGWS object is an in-process server, the memory allocated for that object may not be freed immediately. Within the managed execution environment, the object will remain in existence as long as any managed objects hold a reference to it. If the COM client holds the only reference, the object will still remain in memory until the garbage collector frees it.