Captains decision is final only once the aircraft has motion, until then they or equal to all other decision makers - ground crew, cabin crew ATC, police etc.
Yes at any stage prior to motion they can refuse to carry out duties OR be FORCED not to carry out motion by lets say Mr Branson if he wants to make that call.
Never heard of a pilot to take a cancelled flights aircraft just to get home because the boss cancelled a flight, but heard many of them complain about not getting home that night.
Responsibility is not just a captain thing, but yes at a point it does and only until the next point. Limits apply to all.