I've been wondering something for awhile now: if Hank had never discovered the Walt Whitman book (Leaves of Grass) in his brother-in-law's bathroom, would Walter White have gotten away with everything he did?
Think about it: left undiscovered, Hank would have had no reason to take another look at the Gale Boetticher case. To me, leaving that book out in the open, or even leaving Gale's note there, seems like a careless mistake on Walt's part.
Its hard to say but it is obvious that finding that book was what caused Hank to finally learn that his scumbag brother in law was the criminal he had been chasing all along and was right in front of him the whole time. Hank is my favourite character and seeing him stadning in the presence of Walt before learning of his criminal actiivties is painful to watch.
And Walt having that book out in the open was a careless move, however nobody else, aside from Hank and Jesse would have known the significnce of Gale's wrting at the begiining and I guess Walt thought Hank had given up trying to catch him once he murdered all of Gus' former employees, so he severely underestimated Hank's determiation to catch him.
Don't forget, Hank had given up investigating Gale and thought he was Heisenberg, but Walt drunkenly told him to contiune looking for the real "genius". This caused Hank to re-open the case and eventually led him to evidence incrimitating gus and eventually to Walt himself (the book signed by Gale). So Walt pretty much planted the seeds for Hank cathing him during that dinner. Walt coul'dve gotten off scott-free had his pride not taken over.
So wrapping up here, had Hank not found the book, Walt would have gotten away with it. There was no one else that would blow the wistle on Walt (not even Jesse, to Hank at least), he retired from the buisness, had his money safely hidden away and evenutally would have died from cancer and Skyler would not have ever told Hank about Walt's crimes (she was waiting for him to die all along)