Putin and authoritarian leaders in his position have three primary options for succession.
https://ru.krymr.com/a/29113403.html
https://www.gazeta.ru/politics/2018/03/21_a_11690251.shtml
https://politeka.net/blogs/621092-ne-te-putin-multiki-smotrel/
http://www.ng.ru/politics/2018-03-21/1_7194_gudkov.html
https://newtimes.ru/articles/detail/154120
https://newtimes.ru/articles/detail/154241
https://politeka.net/politeka-onlajn/620960-illya-ponomarov-pro-rosijski-nevibori-ta-strah-kremlya/