When they begin the rebuilding and clearing the site of burned/melted material they could package up small pieces and sell them to collectors. Like they did with the Berlin Wall.
Would raise money and keep all of this history from a landfill somewhere.
Agnes, I pray that you have a friend in Paris who can share your idea with someone who has the contacts to spread it around. If there is one tiny shard of one of the windows left I would so love to have one.