Apparently, he had tried to resign his post 2 times in the past, but the Warren Buffett and the board of Berkshire convinced him to stay. Given the seeming allegations of insider trading, this doesn't look good for Berkshire.
While we don't have the facts on the matter, there should be nothing wrong with simply having dinner with a CEO, buying shares, and suggesting to your boss that they might want to do the same. We have no idea what was discussed at the dinner, and should be slow to come to a conclusion until more facts come out.
This instance does act as an example to show people that over reliance on the reputation of management is not good. For example, most people have in the past, thought that David Sokol would eventually become CEO of BRK... obviously, this isn't the case, and should suggest that succession plans are not as firm as one thought.
More importantly, one must also question the thinking of the board of BRK, in that if Sokol was actually on the list of candidates, why did he remain on it, when he had expressed interest in resigning 2 times in the past... It seems that it would be a red flag that the guy might not want to be there forever.
Having a few core people that are integral to a company can be a double edged sword... they generally work well for a while, but, when they leave, it is very troubling. At least they still have Munger, Buffett and Jain! With this said, BRK is set up pretty well, and has a huge pool of able managers to draw from.
Disclosure: None. This is not advice of any kind. Always do a ton of your own research in regard to anything that I say, write, or so much as even think about.