Yes, but just replacing 20% of those 21% slots with widebodies in Saudi and possibly more new carriers. This would equal the loss!
Looking good on the long-haul front, lets hope we see a further increase in flights to the East, such as China and India. These are the two biggest growing economies, and if an airline such as Jet Airways (which have shown an interest in MAN, BHX and NCL) can drag the LHR connection passengers away from BA, MAN could regain 3rd spot before long! Anyway...with the airport's view of 42.5 million by 2015, they will certainly need to attract more airlines!
Will another terminal be needed?