Apologies if this has been covered in an old thread. I am fairly sure it has been covered in one of the "get champagne for free" threads, but I can't find it...

What is the latest acceptable cancellation on a full flex ticket? If one checks in, goes through security and then is called out on an emergency, misses the flight, and the cancellation of a ticket receives sort of priority 283 due to the emergency - will BA still accept this ticket for a refund the next day or possibly even later? If yes, what is the time frame of the ticket expiring? One year after it has been issued?

(I'm not asking for a "sympathy due to emergency refund" - merely want to know what the rule is).