Based on an A320, four aircraft removed for a six month summer season is circa 790,000 seats out of the program.
Sorry to be pedantic,but your sums aren't quite right
A4.
Each short haul aircraft will average 2.5 rotations per day, 180 seats per aircraft = 1800 seats per day (packages are sold as round trip so you can't count seats outbound & inbound separately). For a 182 day summer season that's 327,600 fewer round trip seats.
Statistics aside, this is another sad day for people in aviation. The guys and girls in TCX have been through this too many times now. Moral must be at an all time low.