I am not sure how much removal of the A320 will affect things. Monarch did not seem to fly a full five aircraft programme last summer; Their aeroplanes are only committed to two rotations on many days anyway. Remember the fifth aircraft was bought in at quite short notice when EDI was dropped and may have been a best use option rather than a careful choice.
I would have though a few extra Wizz and EZY rotations could make up the difference.
With the demise/absorption of BMiBaby and FR lack of enthusiasm enhancing at BHX looks like a smart move.