If you assume that all of the money for that gas and oil can be spent on the war, perhaps. But I read recently that Russia's had to reduce the taxes on oil/gas

If you assume that all of the money for that gas and oil can be spent on the war, perhaps. But I read recently that Russia's had to reduce the taxes on oil/gas production nearly to zero to make the new fields at all profitable, so I doubt that all of that money goes to pay taxes to the state. Mostly Europe's money goes to pay for actually producing the oil and gas sold. Not all, of course. Old fields are cheaper and still taxed at considerable rates. But the state had spending for that money before the war. Can't cut pensions to zero.