Damn shame, surprised there wasn't effective watering systems in place like in many historical churches.
Thankfully they're gonna most likely reconstruct it exactly like it was since it's such a historical masterpiece. I went to Teatro La Fenice in Venice last year and couldn't believe it burned down completely in the late 90s and was reopened in 2004 as almost exactly like it was. With the Notre Dame there is going to be 100% accurate laser scans done on every single surface so the regular lad won't see a difference and it can be restored to almost exact historical accuracy (just google Notre Dame laser scans and you'll see what I mean). Of course the authenticity suffers, but you'd be suprised on how many times most of the legendary pieces of architecture has been destroyed and rebuilt.