Sad news indeed for anyone with current or former Manston connections. Unfortunately, if it does close I feel this has been on the cards for many, many years as successive operators have attempted to make it viable but failed.
For me, Manston has always had more potential as a cargo field rather than with passenger ops. In the early 90's, while it was still RAF Manston, a civil operator tried to combine two poor passenger catchment areas by flying from Gatwick to Norwich and then RAF Manston for pick-ups before delivering the passengers to Cyprus. The following week, the jet reversed the route, dropping off at RAF Manston and Norwich before flying empty back to Gatwick. This lasted only one season (B737).
While in RAF hands, you would have to go back quite some time to see any operator using the Civil Enclave (commonly known then as Kent International Airport) who would have generated enough traffic to sustain the airfield had the RAF not owned and maintained it.
Since the RAF departed, no major operator has been sufficiently tempted to use Manston for anything truly meaningful over any extended period of time, so I think it's unlikely to happen now although it would be something I would be very happy to see. The fate of TG Aviation is quite rightly a worry as are the jobs that would be lost (about 150). The two museums are also on airport land and could also be at risk.
Hoping for a good outcome.