Selling only natural gas, even at very expensive prices, doesn't get you anywhere, long term, Putin knows as much that's why in the last few years Russia tried to make a conscious effort not to depend on oil and gas as an economy anymore (if I'm not mistaken the share of oil&gas in the Russian economy has gone down from about 14% to about 8-9% in the last few years, I'm too lazy to search for the exact Economist article where I had read that).
> Russia only has a tiny economy compared to China, so if China decides to play games,
From Putin's perspective, or whomever will take his place, it's better to be at China's mercy compared to being at the West's mercy (as present economic sanctions demonstrate it was the case), as in China and Russia are a lot more close, ideologically speaking, compared with how Russia and the West compare. And Russia still has and will have nukes, there's no way for China to take some piece of Russia's Far East (which I know you didn't mention but is a point often made when it comes to the Russia-China relation).
> Russia only has a tiny economy compared to China, so if China decides to play games,
From Putin's perspective, or whomever will take his place, it's better to be at China's mercy compared to being at the West's mercy (as present economic sanctions demonstrate it was the case), as in China and Russia are a lot more close, ideologically speaking, compared with how Russia and the West compare. And Russia still has and will have nukes, there's no way for China to take some piece of Russia's Far East (which I know you didn't mention but is a point often made when it comes to the Russia-China relation).