There is an additional element to this question that I have not seen discussed previously in this thread, or any other threads. Demonstrating one's commitment to living and fully being in France.
As many have pointed out, you can live with a RHD vehicle in France without major problems. Some have even noted that on difficult mountain roads, RHD might even be safer, since you have a better view of the edge of the road (and the void below).
However, the mere presence of a RHD car in France, especially when it still has UK registration, loudly states I HAVE NOT INTEGRATED INTO FRENCH LIFE.
And, in fact, that is often exactly the case. More than any other expat community Brits (dare I say English) are known to, or at least strongly suspected of, clumping together into little enclaves.
If you have decided to move your physical life to France, but you are not ready for total immersion, keeping your RHD vehicle will loudly broadcast your intentions -- Regarde, les Anglais sont arrivés.
On the other hand, adopting and adapting to the values, habits, ways of life, etc. of your new home will likewise signal your openness to commit to fully accept all the consequences of your choice.
Dump the RHD.