With the disclosure of an affair, David Petraeus went from God to Flawed Giant. That's not so bad, considering few human beings even make it to a leadership position. Sure, his brand took a hit. He lost a job. But if he can hold onto his marriage to that rock of a woman Holly, all will probably turn out well.
Flawed Giants ranging from John F. Kennedy to Jack Welch still leave a legacy of accomplishments which no one can discredit. Also, they lived or live very satisfying lives. Kennedy got to do exactly what he wanted to and Welch can attract to himself all the attention money can buy.
When the shock of his petty transgression passes, Petraeus likely will apply for or be appointed to some leadership position. He can teach a course on his passion - military strategy. Most importantly he can be the mentor for others who did something dumb and how they can put together a path back home to the giant they were or could be.