"I shall go to the grave, and on the third day rise,
And, just as rafts float down a river,
To me for judgment, like a caravan of barges,
The centuries will come floating from the darkness."
There are a few different endings to Doctor Zhivago, depending on how you look at it. The book's main "story" could end with Zhivago's death, or maybe it could end when we find out about Lara's reported death in a concentration camp. The actual prose of the novel ends with Misha Gordon and his buddy Dudorov meeting Zhivago's long-lost daughter during World War II.
But even though these are both "endings" to the book, Pasternak made a clear choice to end Doctor Zhivago by showing us some of the poems Yuri Zhivago has worked on throughout his life. Even while the world was going to hell around him, he never lost his passion for writing poetry. The most interesting thing about this poetry is how apolitical it is. All Zhivago has ever wanted to do was live in peace and write poetry about nature and people. His society has pressed him to declare where he stands politically, but in the end, all he cares about is living a quiet, free life.
You could also say that Doctor Zhivago doesn't really have a conventional ending at all. We mean, after all, Zhivago himself dies before it ends, and all the stuff about his life after Lara leaves seems almost like a different novel. We don't really know what will happen to Tanya, Zhivago and Lara's daughter. In fact, we don't really know what has happened or will happen to Tonya or Katenka or Zhivago's other children. Things are left pretty open.
Russian novels are actually famous for having open-ended endings. Take War and Peace, for example. The war ends; then some characters get married; then we find out in an epilogue what happens after these characters get married; then we get, in a second epilogue, a straight-up nonfiction essay about history. We're not making this up, folks. We couldn't make this up.
Some people say that Russian novels end like this because it's the way real life is: we don't usually get neat, packaged endings with all the loose ends tied up. For a novel that's so into the idea of life and living it to the fullest, maybe it's appropriate that the ending tries to leave this open, real-life-style.