How do you sack someone who is not at work?
In these circumstances, where BA has had to put up with this behaviour for such a long time, I suspect that those that don't show up on day-one of the strike will be contacted by phone to see why there has been a no-show. If they don't reply, perhaps a courier-delivered letter stating that the lack of contact (either employee-to-BA, or BA-to-employee) leads BA to think that a breach of contract has taken place and said employee has entered the process for dismissal.
Claims of illness will be looked at very closely, I'm sure, but those with a 'history' will be walking on thin ice. Won't take long for word to get around, but by then 'martyrdom' will have claimed a few, who will be giving marching orders. Cue the usual hand-wringing from BASSA and claims of bullying and the like. By then it is too late - BASSA and Unite will have well and truly used up their pathetic 'arsenal'.
But this assumes BASSA and Unite have the guts to step up to the plate. I don't think BASSA and Unite will, because they know they have screwed up royally, and day-one strikers will be in line for firing! Will it get as far as a strike? I don't think so, regardless of whatever showpiece ballot they care to run. They don't have the spine to do it.