Cancellation of Russia as the heir to the USSR - and hence, its seat on the UN Security Council - would not prevent Russia from separately applying for ordinary UN membership like any other state with global influence or nuclear weapons such as India.

Of course, Russia would have to agree to the goals of the UN Charter in order to acquire a seat in the UN General Assembly. If it really followed those goals, Russia might even get one of those temporary non-veto 2-year seats on the Security Council.

And if Russia doesn't support the goals of the UN Charter, its absence from the UN would merely prevent its continuing obstructionism.