Realistically I can see aircraft being allowed to fly with the middle seat in a row of three being empty, ie 120 seats available in a 180 seat A320. Those in window seats board first, then those in aisle seats. Whilst this would be uneconomical it might be sustainable for a short while. Those travelling would only do so if it was absolutely essential and would need to understand the need for a higher than normal fare.
There are some way out of normal fares and routings showing up on the search engines at the moment with all the groundings and restrictions. Results that were previously right down the bottom of the list and you wondered why they even bothered to show them due to the travel time and cost, are now all that's available.