It will be an adventure, whatever happens birkin-wise. You wouldn't be the first person to wing into Paris for a two day shopping expedition! And, whatever happens, if you don't get the bag on this trip, you'll learn more about the process of getting the bag just by being on-site in Paris. It's true that it will probably be something of a nerve-racking experience: will you get an acceptable bag or not? But that's what makes it an adventure, b/c you just don't know what will happen. It sounds like other people get birkins all the time in Paris so why not you? I'd think positive about this, don't give up on the idea even before you get to Paris.