My guess is you will get a letter saying that the incident has been investigated and the cabin crew report checked.
That they are sorry (without admitting any liability) and that as a gesture of goodwill a travel voucher is enclosed for GBP 250.
Your reference to an upgrade to Club/First will probably stop them from including an upgrade voucher into the deal.
Unfortuanatly BA Customer Services do not respond well to what they will see as a threat. They also do not respond well to clear demands for compensation.
My guess is that they will make to exgartia gesture as above and accept that they have lost a customer.
Nick