magnitude of IQ signals from IQ demodulator

How is the magnitude of both I and Q outputs of an IQ demodulator calculated if say, the two inputs to the IQ demodulator have amplitudes A and B? Is it half the product of A and B for both I and Q? Do I and Q share the same amplitude always?

A real world one? With diodes in it? It is calculated to be the lesser of the following:

the input signal minus the conversion loss
the breakdown voltage of the schottky diodes (ie. limited to perhaps .25V max)

What if I have two equal in magnitude signals (say 50mhz) going into a IQ demod...what are the magnitudes of the I and Q outputs then?