A very reliable barometer to show whether a particular airport has a large enough population catchment area [the watershed area between other nearby passenger carrying airports] to be a viable passenger carrying airport in its own right are the domestic terminal passenger numbers. Holiday flights and European flights are often subject to much more complicated and often long term funded deals even though the particular flights may be heavily loss making.
Bearing in mind that DSA is right in the centre of Britain, if the catchment area population was big enough, then these domestic flights should be pretty well patronised. Flights to Glasgow, Aberdeen, Edinburgh, Cardiff, Belfast, Inverness, Exeter, Southampton etc. Even allowing for Doncaster's good North South rail connection [which Manchester and Leeds also have] these flights would be well used. The March 2017 figures show that DSA has less domestic passengers than Both Teesside and Humberside (for example) and has dropped 14% since March 2016.
I also notice that a lot of the Eastern European routes have double digit percentage drops in passenger numbers since March 2016 [as we approach BRexit].
I also notice that after a blaze of glorious announcement in Winter '15 Flybe are down to 1 small Emb. jet.
Without true passenger demand airports will only work if they are funded. I expect the funds to keep flowing.
Yorkshire losing millions upon millions of its passengers to EMA, NCL, MAN, LPL etc- under gigantic competition attack from its neighbours, so
DSA [small catchment] + LBA [short runway on small hill top - cut off from M1/M62/Trans Pennine Express/East Coast Mainline/South Yorkshire] = Booming MAN
I have absolutely nothing against DSA just as I have absolutely nothing against LBA (where I am based) but this strategy of nonsensical Yorkshire infighting only helps every other airport that surrounds Yorkshire.