If the generator has control electronics be certain it is still supported.
Exactly. We can maintain quality of life running the generator 4 to 8 hours a day (or less) in a catastrophic situation All we really need for survival is water so we could just run the generator to refill our 2,000 gallon water storage tank from the well.400 gal x .7 gal/hr = 280 hrs of run time
280 hrs ÷ 24hrs/day = 12 days of fuel.
I'm missing the 3 months completely isolated part. Are you going to ration the run time to stretch it to 90 days?