Prigozhin, the head of Wagner, said publicly that the war was waged on false grounds. In response, the Russian Army shelled a bunch of Wagner soldiers, killing many of them. Now, it seems like fighting is starting between Russian Army soldiers and Wagner soldiers around Rostov.
“FSB opens criminal case after Yevgeny Prigozhin accuses Russia’s military of attack and says ‘evil’ leadership must be stopped”
“This is not a military coup, this is a march of justice" – Prigozhin, head of Wagner
A change in leadership/government doesn’t mean Russia will cease to exist.
But it’s a very interesting question. Here’s the UN article on elegible members:
https://www.un.org/en/about-us/un-charter/chapter-2
(note the: “Membership in the United Nations is open to all other peace-loving states”)
It would be difficult as Russia has Veto power, but it can be temporarily suspended if they are under “deliberation by the security council”. This article explains how it might be possible:
https://thehill.com/opinion/international/3717566-how-to-expel-russia-from-the-un/
The consequences of an expulsion would be worth considering as well!