Corporate boards do have quite a few legal obligations to their shareholders. The often-mistaken popular view is that companies are required to seek ever-increasing profit above all else.

While that isn't true, if a corporate board takes actions that are contrary to shareholder interest, they open themselves to liability. In the case the GP is talking about, where a buyout offer exceeded any amount of return that the company could possibly provide while remaining independent, shareholders would absolutely have a case if that acquisition offer had actually been turned down.