The whole idea of the sanctions was to appeal to the oligarchs pockets. Putin built a $600 billion reserve(you can find articles about this going back months/years) and secured deals with China already. There is zero chance the oligarchy will turn on him now.

Here is a rundown of his reserves. 20% of it is gold which is the 4th biggest in the world. That reserve is about 17 months of export revenue. He will be fine. He planned for the long term already.

The only remotely plausible scenario I see a coup is somehow NATO joins the war, it goes nuclear, world calls for peace and he refuses for whatever reason.