Who is most likely to take Putin's place?
Dmitry Medvedev is a likely choice. He's supporting the team right now but if he were the boss I think he would change his tune in a hurry.
Medvedev was then appointed by Putin as prime minister. He resigned along with the rest of the government on 15 January 2020 to allow Putin to make sweeping constitutional changes; he was succeeded by Mikhail Mishustin on 16 January 2020.