I know this is going to be an unpopular opinion but I don't really think this is THAT big of a deal. Yea, I know the art is old and all that and it really is unfortunate but its also the nature for all things to change. Maybe in another 30k years, we'll be looking at the defacement as an amazing piece of art that tells the story of the current social climate at this point in time, or something along those lines.
Yes, it IS that big of a deal. Anything 30K years old made by humans is precious beyond measuring. We don't have written words that old. The stock of them is strictly limited and there won't be any more (unless someone discovers one somewhere else, which will be world news).