There’s only one variable which will effect the speed of recovery of this industry: Widespread immunity from this virus. Either acquired via having recovered from an infection or by application of a vaccine.
As for acquired immunity? Presently it’s the best kept secret - no where is there even educated speculation on whether it exists or not. And the vaccine? I’m reading it’s two years away.
While the global population remains susceptible to being infected there will be lockdowns, border controls etc none of which is good for the airline business.