John Dean claims (in this story) that, if Model Rule 1.6 had existed at the time of the Watergate break-in, President Nixon would not have been forced to resign. Dean, who was disbarred for his role in the Watergate scandal and who now teaches CLEs on legal ethics (as an aside, see here), reasons that he and other lawyers would have been in a stronger bargaining position if they had been operating under Rule 1.6. In particular, he appears to argue that Rule 1.6 contains confidentiality exceptions that would have been triggered after the Watergate break-in and that the disclosure option would have enabled the lawyers to shortcircuit the coverup that led to Nixon's resignation.
I'm skeptical that Rule 1.6 in its current form would have affected how the Watergate scandal unfolded. It seems to me that the institutional dynamics were such that it would have been very difficult for a lawyer in that circumstance to have threatened disclosure in order to encourage appropriate conduct, let alone to have made an actual disclosure. I've written about similar issues here. Moreover, if a lawyer (like Mr. Dean) didn't like what he was seeing, he did have another option that was ethically appropriate at the time: he could have resigned.