Herman is still unproven himself. He is getting beat by Navy as we speak. But he will probably get paid a bunch of money by Texas soon.
As far as a proven replacement... not probably going to find a proven HC that would be willing to come to ND - whatever proven really means anyways.
Make a run at a guy like Venables, get an innovative OC who understands how to manipulate defenses but isn't afraid to line up and punch you in the mouth running the ball, hit the recruiting trail and weight room, and see what happens. I would bet that after seven years, the program would be better than where Kelly currently is seven years in.