Firstly, let me say that I have no vested interest in Manston remaining as an airport or being closed. Sentimentally, I would like to see it remain as an airport- & a profitable one at that.
However, I cannot agree with Roger Gale's reasons to keep it open.
There is no likelihood of Manston playing any part as an "overspill" London airport until whichever new development ('LL or 'KK) comes on stream.
It may well be the "Base of Choice" for SAR; but, neither that, training flights nor being a "Master Diversion Airport" is going to pay any of the bills necessary to keep it open.
Is it not the case that aircraft which need to divert in emergency situations do not pay landing fees ? I'm not sure, but I thought that was the case.
The other prospect is freight. Manston has already tried that &, as far as I am aware, failed.
The only income stream that could keep Manston open, & profitable, would be some sort of housing &/or industrial development on a large part of the aerodrome.
Those who advocate a successful future solely as an airport are sadly disillusioned !