I doubt the resignation has to do with Benghazi. Plus he can still be called to Congress. Which I doubt he would take the 5th and not appear.
Although, I would Note that with the trial of General Sinclair. That Sinclair has stated if he was going down so were others too. Which does bring me to the point of noticing that Several Leading Generals that are Republican have been removed from command or have been in the news with some issue. McChrystal, Sinclair, Couple of other TOP Flag Officers as well.
Moreover has anyone got word why Rear Admiral Gaouette was pulled from our Battle Carrier Strike Group in the ME? As I have hear he has been accused of inappropriate leadership judgement. Which I would have to question this charge being thrown at the Admiral. As well as some charges that have been thrown at some Generals.