I dunno, BBB. Mr. Walsh has often said he has no problems working with Unite--only with BASSA.
As an industrial relations consultant, I would never advise a client like BA to destroy its working relationship with Unite just to end a problem with their sub-group BASSA.
If Mr. Walsh damaged Unite badly with a law suit for damages, he in effect would be damaging his own employees and taking their money they paid in dues, thousands of whom belong to Unite as part of their other negotiating groups (who have all reached agreement with BA on their own staff and pay reductions.)
That wouldn't do BA any good, nor solve the BASSA problem....
BA has a problem with a number of its cabin crew employees and BASSA. So they will probably focus on that problem. Not punishing the parent organization who did its best to come to an agreement--which BASSA reps refused to present to their membership for a vote (as did CC89.)
Mr. Walsh knows that BASSA also called the strike last time when Unite had not done so, seemingly behind their backs. If I recall BASSA called the strike, which I believe they have a legal right to do on their own, even though Unite was trying to do further negotiating at the time and did not sanction it at that moment.
So in a way Unite has done what it seems is in their purview so far. But BASSA/CC89 are the recalcitrants.