I think the LGW numbers will continue to hold their own, although there obviously will be an effect (and we may lose a rotation or two) I believe that BA in particular has a strong enough customer base in the Island to ensure things don't go too far downhill.
BA announced recently that they would increase the number of rotations per day to LGW would increase from 5 to 6, so there is obviously the market there.
All the best to bmi... and good luck!