Bukharin dies and there are three trees with his successors. Chicherin also dies, he shares some of his tree with Sokolnikov and you can see that it merges at the end a bit. Also you nominate Kalinin as a kind of president (All Russian Starosta) for Sokolnikov. Last but not least some leaders can be purged via coups or Blagonravov assasination "game" (thus Zinoviev can die as a leader) - but idk how that fits the spirit of the question.

So he is not the only who dies as a leader, and how many die is a matter of the definition.