I think plenty of people have known who Bansky is for years, but does it really matter. His art can make people think and that's what it should do. It can just be a hassle if he paints on your property.
Graffiti can stray into vandalism, but there are places where street art is accepted and celebrated. I guess some prefer to be more outlaw about it.
I would think if Banksy hits your property it's almost like owning a valuable piece of art.
Maybe hire contractors to cut your wall out and preserve it lol.