If you do not belong to a union and have a disciplinary then you are on your own.
I don't think this is quite correct. I recall from a past employment that you could be accompanied to a disciplinary or any other confrontation with management by another employee or by a recognised representative of your trade union. the "accompanying employee" need not be a lay member of the union to which you belonged, but could be anyone on the books.
On a different theme, as fairly frequent SLF, I have noticed that BA will credit EC members with the tier points for any flight they are booked on that is cancelled because of the strike (assuming that it is going to happen), as well as giving a full refund. That effectively removes the risk of booking, and even goes a little bit further.
I seem to recall that around the time of the first ballot there were suggestions that it had multiple legal problems, not just the one BA took to court. If this is true and the other faults are still there, will BA go to court again, or will they call BASSA's bluff and let them have their strike?