When this first started there were a few shuls still open and I was told that as long as at least one shul in the neighborhood read the torah, there were opinions that this was good enough.
As the backup gets larger and larger, I suspect something along the lines that there would be one minyan of 10 men who would read all the missing leining for the entire community however long it takes. Perhaps with a fast reader as it could be significant and change Baal Koreh so people go eat, rest room and other needed breaks. but if the Minyan started around Netz and countinued until Rabbenu Tam time, you could probably do most of the missing in on Shabbos