Oligarchs don't have the ability to overthrow Putin.
FSB is the only entity in the country with the power to depose him and they seem to be thrilled with the prospect of a new iron curtain.
Not quite..but there is a strong chance of a military coup....
Reading an in depth report in my weekend newspaper that various Russian Generals have been vocal in their disapproval of Putin's balls ups! Basically stating
"we should have turned the Ukrainian airfields into a lunar landscape by now" & other stuff. they wanted to hit harder..Putin's held back (tried to see how far he could go without upsetting UN/EU/NATO & blackmail everybody over the oil/gas..& that option has now NOT worked 100%!)......plus they are pissed off due to the previous "humiliations" in Afghanistan & Chechnya.....this latest humiliation in Ukraine isn't going down to well with the military top brass..
Putin's not listening to them, & has sent the head of the army to the eastern front to sort it out...& possibly to be killed....how many more General's etc will die before they stage a coup is unknown...
One of the main reasons they are pissed off is because if/when Putin declares it a war, then as per many other countries, various legal/gov plans/laws come into being....& in their case, more conscription & for longer, martial law, & various self protection mechanisms...& the military wanted this stuff in place sooner..not later..
It does appear that Putin made be forced to declare it a war on May 9th, (Russian victory day against the Nazis)....