I feel I should point out the entire country is a hotbed of really cool old castles and churches, and while Notre Dame de Paris was famous due to the hunchback (victor hugo) and its relatively accessible paris location, I've seen way more impressive outside of the capital... Reims comes to mind and that was damaged too - Orleans is not bad either... If you wanna help, go visit outside of Paris !!
If you are into old stones and medieveal stuff, do yourself a favor and check out Carcassonne ! The food (duck cassoulet) will also knock your socks off and there is still an entire fortified city, it'll blow your mind !
To me this is 10x cooler than notre dame ever was...
Also, on another note, 400 mil euros are already pledged, which makes me wonder why the vatican isn't jumping in. God knows they have a stake in the church, a lot of money, and a lot to atone for (sex scandals), that would be a great start and a good
PR coup !