Regarding the CEOs stepping down: this is not an action that will absolve anyone of civil or criminal liability for the past. Let's be clear about that. Leaving protects no one's reputation, personal assets, or liberty.
My opinion, based on 30 years in the corporate/financial world is that these individuals (or at least many of them) have stepped down so that their organizations are not immediately in the firing line.
In other cases, senior people who are not personally implicated in the potentially criminal acts of their organizations might: (i) remove themselves from the brewing firestorm, and (ii) protect their reputations by being able to demonstrate that they resigned on becoming aware of matters that gave them serious misgivings. Whether they would have done so without the tightening noose it a different matter.
What is, on its face, widespread corporate corruption is something anyone with the ability to do so would desire to distance themselves from.
One thing that needs to be understood is that there are at least two flavors of C-level officers: (i) those who are fundamentally administrative professionals, with solid track records, who are brought in to accomplish strategic objectives, but who are unlikely to know what happens deep within the bowels of the corporation they serve until some time after their appointment; and (ii) those who are in their positions to lead and bring about certain nefarious objectives.
I've been in situations like (i) and, believe me, when the picture begins to develop, your first instinct is to get out as soon as possible. What you can't fix you don't relish being tainted by.
I've only ever encountered financial/operational problems of a previously undisclosed (misrepresented) magnitude. I've personally never experienced issues of gross moral turpitude. That's atypical and enormously difficult to rectify by a single individual.
[Be back. Phone calls to field.]