There is no need to contact the company on strike day, I'm sure they'll be able to work out whats happening.
Be aware that once the ballot result is announced (more than likely in favour), based upon previous disputes BA will contact you directly prior to the first strike day, whether you are rostered to work or not and will ask whether you are intending to strike. They need to know in order to plan accordingly. There may be a legal obligation for you to answer - BASSA will know. That said, any answer other than "No" will be taken to be a "Yes". Only those who are long-term sick, on leave or downroute will be exempt.
If you are downroute,
provided you are prepared to operate back if an aeroplane appears, you will not be considered to be on strike until you arrive back at base. Take my advice, you
do not want to go on strike downroute!
Make sure you get
all the advice.