This has all been covered before in the previous threads. However, BA will be on the look-out for 'pattern sickness' - go sick on the day of a strike and you had better have a genuine reason!
As to numbers, BA will establish how many intend to work (it will be a high %age) and crew the flights accordingly.
BA can switch crew reporting for a flight to another flight at a moment's notice anyway.
Where were you flying to?