Normal UPSes only last so many minutes. You are better off putting servers in multiple regions but getting that right is not trivial.
There's generators that use natural gas, and they automatically turn on when the grid goes out. A UPS can be used between that and switching between the gas generator and the electric grid. Though, generators that use natural gas are less efficient and more costly than electricity from the grid. At least these are meant to be used only during outages. However, for a reliable power supply, it would be great.you're more likely to find diesel-powered backup power generators at soccer/football stadiums than at datacenters
There's other brands too, like Trane, Briggs & Stratton, Kholer...