I honestly think this is what's really happening.
As stubborn as everyone says he is do you really think he will quit?
Everybody has a breaking point and if Harlan is making these hires and it's true that the next OC or Dc could be a coach in waiting it's possible he pulls the rip cord and follows Harbaugh to his next gig.
After typing that, I agree he's too stubborn to leave on his own....