An awful lot of oligarchs and other powerplayers, including a few who were affiliated with the Siloviki, have "committed suicide" or "had heart attacks" in recent months.

Honestly I think if Putin pulled out he'd be fine -- most of the opposition is dead, running scared, or on his team. A lot of Russian assets have been frozen, though, and if he wants to get those back he'd have to walk away from his 2014 gains, or else justify why all of that $$$ is gone.