Mikhail Mishustin, the Prime Minister of Russia, takes over if something happens to Putin.

Edit: I'm not implying he was on the plane. Just an FYI for people.

Edit2: Mishustin would be temporary and wouldn't have much power. The true successor would come from the "siloviki," Putin's close confidants from military/intelligence circles. Probably Nikolai Patrushev, ex-KGB warhawk.

Mikhail Mishustin, the Prime Minister of Russia, takes over if something happens to Putin.

Edit: I'm not implying he was on the plane. Just an FYI for people.