I just Googled “Images of Notre Dame stained glass windows,” but my computer is acting up and I could not paint the URL to transfer here. Look them up yourself. There are many different kinds of windows there. Some but by no means all have been destroyed. The glass parts are connected by double sided grooved strips of lead called “came.” Being of lead they are very susceptible to melting from heat. I also understand that the spire that fell had many tons of lead in it’s construction. Probably also melted and fell.
Regarding the formula. The church (Vatican) may have saved these formulas. Or perhaps the guilds kept them secret. My grandfather created his own glass colors for his work in the Indianapolis State Library. He also experimented with interesting effects. I have seen one glass he produced that was iridescent blue like a Morpho butterfly. Also another that was an iridescent satin surfaced rich gold. I’m sure that with the big money pledged for restoration, that this work can be done, though probably not in 5 years. I heard something like a billion dollars in pledges. Also money is now pouring in for the 3 southern churches that were recently burned.
I hope you are right, that the formulas were saved. Tiffany destroyed them purposely, for commercial reasons, but that might not apply in this case.
Consider what was not destroyed: the apostles, other evangelists, the crown of thorns even if fake, the pieta, and of course the cross.
Note that a freeper biochemist has stated that all of Paris is contaminated with the lead smoke.
I was happy to hear the stained glass windows survived! The heat had to be intense. Cleaning the windows for smoke damage will be necessary, however.