You may still be out of luck. AFAIK most of the latest natural gas water heaters require electrical ignition (I think old pilot light ones can still be found, though).
We get a power outage maybe once a year averaging 30 minutes, perhaps. However we still have plenty of hot water and would still have plenty of hot water even if the power outage lasted half a day.
'19 Model 3 SR+ (own), '16 Leaf SV (leased), '12 Plug-in Prius (sold 3/19), 11.43kW Solar PV (16MWh/yr real production), 20.5 SEER/13.0 HSPF ducted air-source heat pump, 3.70 UEF heat pump water heater, Induction Cooktop, Variable Speed Pool Pump