I hope your husband has a speedy recovery.
i had major surgery at the end of last year and could not fly for several months. I wrote to BA for an extension but got no reply. I spoke to a very helpful lady on the gold line who took all my details and passed it to the appropriate section. I had to send medical evidence- my letter of admission to hospital and follow up appointments. I got my extension which is great. The lady said it’s better to phone than write. Good luck