I think your option now if you don't wish to travel is FTV.

If the FCO advice changes and ABE covers Madeira then I don't see the BAH allowance being of any use to you since it doesn't relate to FCO advice. Obviously FTV would still be available if you decide not to travel at that stage. Also check your travel insurance as it may cover where FCO advice changes to ABE after you booked, although any claim may be limited where you can obtain a voucher.