If Putin throws nukes in Europe then the radioactive fallout will reach border countries including russia. And it could provoke a nuclear reaction from NATO, because nuclear fallout over NATO states could be considered as attack.
As said in many places, Putin will go to history the worst aggressor in Europe since Hitler already. He might have committed economic suicide for Russia already. So don't be so sure he doesn't extend the suicide any further.
If Putin already has decided to end the world in a nuclear war, then there's not much that we can do about it.
But if Putin would be seen as a brutal murderer by many russians, then chance are that there are some who could try to assassinate him, like there were many assassination attempts to Hitler.
