RF Downconversion using Heterodyne Principle after a RF down-conversion using heterodyning principle, will there be an information loss?
If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be retrieved?
Is it correct to say that it is the relative change that matters during demodulation? 
For example for AM it is the amplitude change and for FM its
frequency change and this does not change even if we down-convert to
a fixed IF frequency?
after a RF down-conversion using heterodyning principle, will there be an information loss?


No, if the original signal was band-limited, and the bandwidth of your IF processing is sufficiently large to capture that. (so, if you've built a sensible heterodyne receiver.)


  If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be retrieved?


Yes. Shifting a frequency is just multiplications with $e^{j\Delta_f t}$, and that's an easily invertible operation (multiply with $e^{-j\Delta_f t}$). 

If an operation is perfectly invertible, no information was lost.


  Is it correct to say that it is the relative change that matters during demodulation? 


I don't understand that sentence, but I think you really mean "what matters is the bandpass content, not the carrier frequency", and that would be right. See: equivalent complex baseband.


  For example for AM it is the amplitude change and for FM its frequency change and this does not change even if we down-convert to a fixed IF frequency?


This depends on how you do the AM and FM demodulation – if they work the same no matter the carrier frequency, then clearly yes.