Given that I used Model S batteries, 'greater range vehicles' would account for it rather easily.
Recreating my work:
60 kwh (Smaller Model S battery)
29.7 kwh/day from 10,837 kwh/year
If you assume a 60 kwh battery will be retired to grid storage when it hits 70%, then recycled when it reaches ~40%, then assuming 50% average life remaining gives you ~30kwh to cover that ~29.7 kwh.
actual figures can vary wildly, of course. It might be 'worth it' to keep the pack even when it's only at 20% capacity. You might replace them when they reach 80%. But I figure that 30% degradation during EV use would be about the same time period as 30% degradation during fixed use, making battery durability not a significant factor so long as you're not losing batteries completely to failures too often.
Given the average of 2.28 vehicles per household..., you have enough for 1 day of homes if half of vehicles are electric, if 2 are(leaving ~12% of vehicles as something else) that should be enough to cover the commercial side as well, given that 37% of current electricity production is used by households, 34% commercial, 26% industrial. Some would be made up by batteries from pure commercial vehicles that don't belong to any household. Of course, if 88% of vehicles are electric that would significantly change electricity usage - my estimate was that the 2.28 vehicles would increase the average use of electricity by 50% going by averages for vehicles per household, miles driven per vehicle, miles per kwh, etc...
But I figure step 1 of any storage scheme would be to not charge EVs during a power shortage...
One note that I'm sure you'll love is that in a scenario where most of this electricity is generated with solar panels you'd logically want to charge all these EVs during the day as well. Would make for an interesting mechanic if it became a 'standard' benefit to provide charge for your employee's cars. I'm picturing solar car ports and shades...