Air Berlin operating to STN was always a bit of a tall order, in my opinion. The MAN-LON market is contracting back to where it was before the West Coast Mainline effectively closed down, and connections via STN to Germany were never going to be too popular due to there being so many direct flights from both MAN and LPL.
MAN-STN would still be a very good prospect for Eastern or flybe, due to the premium business traffic between the North West and Essex/Cambridgeshire.