Doesn't look too hot for Newquay either - bad news really for the southwest. Few other candidates will step in other than Flybe for the tastiest routes. Flybe's strategy has always been to eliminate the minnows - especially WOW.
What have the local authority in Plymouth said about their desire to maintain an airport there in recent years? Anything other than resounding support would imply that they see pound signs relating to the redevelopment of that land for other purposes. Sutton Harbour would have to negotiate 'contributions' for local infrastructure improvements in order to gain permission to redevelop the land, but that will be small fry compared to what the land is worth with that permission.
Alas, it's probably the eleventh hour for the airport.