Given there is overcapacity on certain routes, it means the various airlines on said route are running with empty seats, one the the incumbents leaving should therefore mean the remaining airlines can fill those empty seats. Therefore it does not indicate a decrease in the number of passengers using the airport but rather secures the remaining services and makes them profitable or more profitable.
I seem to recall this time last year people bemoaning the future for 2014, and we haven't done too bad, there is still time so lets be patient.