If someone slashes a Rembrandt, people would be aghast if you suggested Banksy stencil over the damage or Hirst submerge it in formaldehyde, no matter how modern and popular those artists may be.
Of course, there are various reasons one might argue the same rationale doesn't apply to buildings.
What is the appropriate repair point? Why should Violet-le-duc’s change be (or not be) privileged over more modern changes? The point of the building was to serve the people of a given time and it was adapted many times over the centuries to different usage models. Even the big plaza out front is relatively new (I have seen historical novels that anachronistically assumed the plaza to have been there, e.g. The Baroque Cycle).
The replacement paint need not be absurdly toxic mercury compounds.
The backing might best be supported by something modern, such as a glass fiber mat.
Likewise with buildings, we can get the old style with modern materials.
Why? The "original" (i.e. the thing that burned) was the result of numerous changes for functional and fashionable reasons over the century. The famous Viollet-lde-duc spire was a recent change only 150 years old. Life is change; cities and old buildings are palimpsests; to try to ape an earlier age is a form of cultural death.
The same is true of the Louvre which has grown and changed in use and shape for 900s years and few complain about that.
Regardless of what happens, the result will disappoint and even enrage many people. Either it will be an attemptt to be authentic, but won't be authentic enough for everyone, or it won't be and that will cause a different kind of outrage. And every change will be mourned by some as a "missed opportunity". C'est la vie!