KLM leaving a route served constantly for over 30 years in favour of a brand new development in an area they pulled out from a few years ago?? If anything they will serve both. Stats show that less than 1% of the South Yorkshire travellers used HUY as a departure airport pre DSA, that suggests to me most of KLM's pax are from the Humber area.
KLM would be blatantly stupid to pull that service, if rumours are true then they will use BOTH HUY and DSA.