SLF question: What is needed to keep the airports open and minimally staffed (e.g. ATC, emergency services, ground handling)?
You mean moneywise ? no idea, but an interesting question .
The quick answer :
(Major) Airports and ATC are part of a State critical infrastructure, like motorways, fire services ,rail and canals..etc... The price tag to do regular needed maintenance and staffing to function , with average traffic is known and cost say X Billions. In the old days prior deregulation , that used to be budgeted by the State and staff were civil servants or employees of companies owned by the State.
What changed is the deregulation that brought a tremendous raise of traffic and that required to expand drastically services, e.g. airports and staff..., cost 3 to 4 X billions and someone had a good idea to have the airlines pay for all that , not only for the extra bits, no, for the whole thing through charges, . As a result Airports and ATC became privatized, and sometime , like in the UK , owned by the same airlines. Everybody believed the Gurus claiming a constant raise of traffic and , the notion that traffic would decrease over a long period of time was disregarded on purpose ( I still have the quotes ..)
Now they are caught with their pants down , and the only solution they found is to pour Billions to maintain the airlines afloat at all cost to prevent the system go from collapsing on them .
This is where we are at the door of winter 2020. Nobody has the miracle solution and everyone is scared of what 2021 will look like.