They have a decent source of their own fossil fuels, and certain deals go through non-sanctioned countries to countries that sanctioned Russia.

They have control of their rouble so they can promise soldiers a big payday and stiff the payment when they went “missing”. In particular their ex-con division.

I’m pretty sure their overall stocks of military equipment are dwindling, as you heard a few high-value targets were downed in the last month that are irreplaceable in the medium term. They still have their own production of tanks and ammunition, and China, NK and Iran trade various equipment to them such as drones, missiles, artillery. They are happy to get whatever Russia has left to offer.

Rich Russians will stay rich for the most part but poor Russians will be stuck in their miserable situation.