It is all up to general assembly vote how they interpret succession of state and whether Russia is a legal successor state to Soviet Union. Ukraine had 'legal equality' to Russia in Soviet Union, so you can argue any of the ex-Soviet republic is also a legal successor, why Russia, because they are the biggest of the ex-Soviet republics and kept most of Soviet nuclear arsenal? They believe PRC is the legal successor to ROC seat (even though KMT still exists on ROC) because PRC was bigger in size/population and had nuclear weapons, so it's all open to interpretation. I'm not saying it's going to pass the vote, I'm saying it's plausible to put it as a draft resolution using the illegitimate successor of states argument.ROC's seat in UN and the permanent membership in UNSC were succeeded by PRC. Similarly Russia inherited from USSR the permanenut membership in UNSC.
To kick Russia out of UNSC it would be a fundamentally different matter.