Walt is now hardened like granite, one of our most important rocks.

No matter what it is that motivates him to go back, I doubt that the show's sense of justice is going to allow him to have his blaze of glory. My guess is he never even gets to use the M60. Gets pulled over for a broken taillight or some other humiliating and mundane shit and that's the end of the road for him.

You may be on to something here, especially considering the scene last week where the Nazis refuse to wear gas masks during Todd's cook.