fiefdoms and private playgrounds, the top management of corporations have a fiduciary responsibility to their shareholders. Although shareholder's employees (aka CEO, CFO VP, etc.) are allowed and encourged to enjoy and enrich themselves, they are supposed to be doing it in a way that enriches the shareholders.
If they reject buyouts that would significantly enrich the owners but put themselves out of a job (with only a golden parachute and a cushy 5 year non-compete/consulting contract) they will be sued...at least if the shareholders find out about it.
Whereas their insurance may indemnify them from mistakes, I doubt it will protect them from deliberate malfeasance. I assume that they have competant legal advice and therefore know this.
So yes, the will be able to get away with rejecting borderline takeover bids. Ones that are wildly advantageous to the shareholders can not be rejected out-of-hand. If the bidder get PO'd and makes it public, the offending management will have serious trouble and hurt the company.