Weeelll, they do still export a lot even to countries that have nominally sanctioned them. Obviously less nowadays than before the full-scale invasion of Ukraine, but China definitely isn’t their only export destination for petrochemicals:
What might screw Russia over is their reliance on Chinese imports, however. Everything they need for eg. maintaining that oil production – let alone consumer products – has to come from somewhere, mostly either from dodging sanctions (making it more expensive and slower) or from China