Since the church was under renovation, many of the priceless works of art had already been removed. I am sure they did lose a lot though. I read where firefighters were trying to rescue large paintings, and they lost many of them. I would guess that the heat from that fire probably destroyed many of the stained glass windows, works of art in their own right. It is a tragic loss for sure.
I hope it was an accident but the facts are, muslims in europe are burning churches. That is a VERY dangerous religion and they are pushing an agenda all over the world, the agenda they learn about in the Quoran, namely death to those who dont worship allah. Unlikely this was accidental IMO...