Unless he has charges pending when he testifies before Congress, he cannot take the fifth without implicating himself in some crime directly related to the cover up.
I do think he “confessed” to this affair and resigned as a way of giving both himself and Obama some cover and possibly buying some time in order for the heat to die down.
Frankly, though, unless Obama is caught in bed with a dead girl or a live boy, Congress is not going to be pressing any serious investigation that might implicate Obama in anything. It’s not in the cards. Boehner is fully on board with Obama’s agenda and nothing will stand in their way.
I agree. Congress is not going to pursue anything that involves Petraeus adultery.
Also, the military won’t pursue anything that their commander in chief tells them not to pursue (or their secdef/secarmy/cjcs/Chief of Staff Army.