I'm sure that if you produce a valid sick note during the days on the strike the airline would not take disciplinary action.
Airline crews have a higher sick rate than most professions, because anything effecting ear/nose/throat means that they cant fly.
As I recall there was a warning prior to the strike regarding calling in sick, but as I said I am sure that any reasonable employer would, if presented with the evidence take a view that it was a genuine sick day.