That confrontation at the end was amazing and Hank punching Walt was satisfying. Hank has suffered more than anyone because of Walt's actions. To play up the Star Trek theme, Hank is facing a no-win scenario.
He might not know who Walt is anymore but he knows how far Walt's reach can go. He risks shattering his family and destroying his career...Hank's not even going to be able to get a job as a security guard because of his connection to Walt. So does he let cancer take his cost (eliminating Heisenberg and preserving his family and job) or does he turn Walt in?
My only complaint is that it was really stupid of Hank to take the book out of the bathroom. Just take a picture of the writing on a camera phone.