Got caught in similar situations twice last year (only one was BA), about 3 and 6 months before departure, though not quite as serious as a Wedding. Unfortunately, the advance customer is not very well covered if the airline cancels more than 2 weeks before travel. For me cancel/reimburse was not a realistic option, so I had to stump up the extra cash for extra nights accommodations plus the other costs.
The point I'd like to add though is I can't find an annual travel insurance that will actually cover this - even those with Gold or Platinum in the title. Any ideas?

Looking at my current policy, it additionally discriminates against 'air mile' bookings too, so I'd best beware of that in the future.