Fortunately, it seems that the only artistic thing damaged was one of the windows. The roof was mostly 19th century, all of the statues in the spire were removed prior to the fire, and all of the stonework is intact.
They just don't make 'em like they used to.
Edit: I stand corrected. The wooden inner structure was from the 12th century and it's all gone. How the hell wasn't there fire suppression built for this kindling? And good god, the roof was made of LEAD.
The roof makes sense. When doing the renovations. Lead would have been cheap and looks quite nice on the building. It protects the wood underneath from the elements. As there was no knowledge of the environmental impact of lead. That wasn't a factor. There is also weight and durability to consider. Lead is dense but only requires thin sheets. While ceramic would be quite thick. Tiles can also break and fall off. Lead roofs have been known to last over 200 years.
The stone walls still stand, but I wonder how much the heat has weakened them. I fear the restoration will take decades at the very least. Vive la France! Vive Paris!
Time would also depend a lot on the process they use. The 19th century renovation took 25 years. It would be interesting if they used traditional techniques. I'd imagine a lot of tourists would be interested in seeing a 12th century style reconstruction with traditional tools and human powered cranes. This would obviously take a long time. Plus the old growth they had back then doesn't exist in significant quantities. So, wood quality will suffer. There also aren't many craftsmen with the necessary skills.
I figure they'll try to recreate it as closely as possible. I certainly hope they don't modernize it. Say with a steel frame and glass roof.