Public debt isn't the problem. As others have said, the problem is corporate debt, denominated in foreign currencies. That can't be hidden by Putin, because the debts are all contracted - & recorded - abroad.Russia is a solvent country; it has very little public debt. I don't buy into any Western Russian economic forecasts. Putin hides much information about the Russian economy, so he and his buddies can steal money.
The Russian government may have to pay them, to stave off an economic collapse, but they may be too big for it to pay.
China could, but what would it want in return for rescuing Russia? And note that being rescued by China wouldn't eliminate the debt, just swap the creditors. Russia would become heavily indebted to China.