Very interesting article on director's duties under the law.
What are directors’ duties and what can they do to protect themselves in a sale of company? : Startup Company Lawyer
In three easy words: it's shareholders, shareholders and... shareholders. A bit longer version: a. make sure shareholders make money, b. make sure you choose the buyer to get the maximum bucks and only that, and c. make sure shareholders know your thoughts, even when you are sleeping.