It does make sense the BA would have to follow a set-down procedure to sack someone under circumstances where there are consequences.
However, given there are no financial or legal consequences as far as the rights of the individual in relation to unfair sacking, they could from that perspective be rather brutal about it - "Here's you letter of termination - the door is that way".
Under normal conditions, they would need to be thinking about union reaction to the breach of the working agreements, however under the circumstances, I doubt they would worry about that. Pointing out that water is wet is likely to be used as an excuse for a strike in the current climate.
As any legal comeback would not allow the individual back in no matter what, the courts would not even allow an claim for unfair dismissal and however they do it, BA would undoubtedly have to go back to court one more time as the union would seek any way to get the individual their job back - as is their role quite rightly. The actual reason would not matter but no matter how they were sacked, as a case would result anyway. BASSA cannot walk away even if logic and the law and advisors are against them.
I still don't think BA would sack anyone on day 1 - just activate the 90 day take it or leave it option.