N7
Why would a military unit relocate to a civvy airport?
The bottom line here is that Peel can make more money from the land as housing / commercial property than they can with an airport. Making money is what they do. It's their airport.
Darlington International has such a small catchment area, bounded by the sea, Newcastle and LBA that there is no prospect of it getting sufficiently busier to survive.
Commercial realities will win in the end. Look at the farce that Manston has developed into, as well as St. Mawgan.