Thanks Tobi and Lisa, even if this topic has been debated certainly plenty of times, it happens to be still difficult to get reliable information on this.

I also wanted to ask this question to the carnet issuing authority and here is my story:

Initially I contacted the French vehicle association and a lady there answered me that if my bike get stolen, then I would have to pay for the import taxes and duties locally, then do the paperwork to prove the theft in order to release my caution when I would be back in France. Being quite disappointed, I asked them several additional questions but at the end she ended the conversation by saying that she was not a specialist and that I should contact french customs - this is why I really thought that she was knowledgeable on this.

Then I contacted the AIT in Switzerland which is the referent authority in the world for carnets. A very nice lady there told me that if my bike got stolen, then I will lose my caution, but I would have to pay import taxes and duties. She did not know the answer at first when I asked and she needed to ask some of their colleagues - this is why I did not consider her answer as being the real truth. She also advised me to contact a lady in the French Vehicle association (again but a different office) whose work is to handle all the related customs claims from foreign countries - I felt like I was converging.

I contacted this lady and she really knew the thing. She told me that she recently handle the case of a guy who broke his engine and could not get the car back to France and the case of the guy who permanently imported his bike in Australia.
She confirmed me that:
- If my bike gets stolen, then I will have to declare it to my embassy, to the police and then go the local customs to get the necessary documentations to prove the theft and to prove that the local customs will not claim taxes and duties to the vehicle association in France.
- She also confirmed me that the local customs cannot claim for payment of taxes and duties and they anyway cannot claim for more than the initial caution amount.
- She also mentioned that it can be also quite difficult to get these documents in countries like Iran, Pakistan and India. Difficult but not impossible as she would give me good local contacts in the local vehicle associations in case something bad happens during my trip.

After hearing at least 4 or 5 different information on this, it was such a relief to get an answer from a very knowledgeable person in charge. It will definitely influence my bike choice (converging on R1200GS Adventure... Hopefully).

Thanks a lot again for your help. Feel free to comment!

Seb.