........When crew duty limits start to impinge, there are both union and legal limits to be considered.
In both cases it's the Captain's responsibility to gently and tactfully obtain the cooperation of the cabin crew in obtaining a sensible outcome. The cockpit crew's negotiated scale of duty limitations tend to be more flexible, although busting legal constraints has to be justified robustly.
Also on short haul there will be only two, or possibly three of them in the cockpit, and consensus is simple. The cabin crew, on the other hand probably are more affected by being on their feet, and in many ways more stressed by external forces such as passenger service, and generally being more out of the operational loop.
When the Captain approaches the cabin crew for their cooperation in assessing whether or not they remain sufficiently fresh and awake in order to throw the doors open and monitor an evacuation, squirt an extinguisher, or police drunks and suspicious-looking foreigners, he may not always get the answer he wants. Long-haul cabin crews can be trickier, as they will have a Cabin Service Director plus a hierarchy of Pursers with opinions in each cabin. Short-haul cabin crew numbers are smaller with a higher probability of hot dates and baby-sitters to consider if it's a day trip from base and not a 'tour'. Other considerations, such as that day's final schedule out of somewhere like Damascus or Pyongyang might come into play, when it comes down to a final assessment of fatigue vs duty overrun payments......(.not that I'm suggesting that BA currently operate to DAM or FNJ )
The cost of operating two aircraft on positioning sectors in terms of equipment disruption, fuel, maintenance schedule, extra crew time, navigation, landing and handling fees are likely to be mind boggling, and taken together with the collateral damage and disruption caused will be closely examined, I suspect. The lead hand in the cabin crew will hope to be on firm ground, as will others who took decisions that day.
Which ever way you look at it, treating passengers that way by cancelling a short sector is a disaster, and is bound to risk being viewed as indifference by the wider public. It takes only the news-hounds to pick up on a 'human interest' story, such as someone stranded whilst rushing to a hospital bed-side, to do immense potential damage to any airline's reputation, and whatever justification is paraded, it is bound to appear plain mean.
Of course it's always possible that an ops decision was taken at base that over-rode the Captain or the cabin crew, but it still is an un-happy event......