That's not that simple. Now RUR is needed only by Russians, so the EUR/RUR rate is completely controlled by the Russian Central Bank and for some unsignificant part by the demand on the Russian market. If EU will have to somehow obtain RUR to pay for Russian resources, there will be second significant source of demand for RUR. Since demand will be larger and if Russian Central Bank will not "print" more RUR the price of RUR in EUR will grow.

That's not that simple. Now RUR is needed only by Russians, so the EUR/RUR rate is completely controlled by the Russian Central Bank and for some unsignificant part by the demand on the Russian market. If EU will have to somehow obtain RUR to pay for Russian resources, there will be third significant source of demand for RUR. Since demand will be larger and if Russian Central Bank will not "print" more RUR the price of RUR in EUR will grow.