Ra Diaz is a hell of a bassist but in my opinion Fieldy is irreplaceable. Fieldy has his own unique approach and style and if you ask me absolutely no one can replace him. However, at the same time, I would absolutely love to see KoRn let Ra Diaz write and record bass for their next album. Why not? The guy studied Jazz bass for many years in his home country, he would lay down some amazing bass tracks for KoRn, I'm sure.