It's difficult to know exactly what to call the "point of no return" in the novel. Perhaps it comes early, with the initial debate between Bazarov and Pavel. Maybe as soon as the two proud men begin arguing, one knows that the conflict can only escalate since neither is going to yield ground. Perhaps it doesn't come until later, with the duel between Bazarov and Pavel. By this point, they're no longer flinging words at another. They're shooting to the death. Yet, we think the key moment actually comes when Bazarov professes his love to Anna Sergeyevna. This is the event that turns Bazarov's life upside down. From here on out, he seems to have lost his sense of purpose and direction. It's an open wound that he can't heal.
Perhaps at no point is the possibility of resolution as distant as when Pavel raises his gun and aims directly at Bazarov's head. At the same moment, Arkady is off at Nikolskoye, though he doesn't even know why he went there in the first place. It's clear that something is building in both of the young men – that the climax of the story is near – and yet it's hard to imagine how the situation could possibly resolve itself. The spirit of light-heartedness and youth that is present at the beginning of the novel now seems gone. Both Bazarov and Arkady are making the decisions of men, whether or not they are ready for them.
After the duel and Arkady's proposal to Katya, the rest of the story seems to simply slide down a steep slope. By this point, Arkady and Nikolai's happy endings are secured, while Bazarov seems more lost than ever. The reader senses that Bazarov is headed for disaster, but it does not become clear exactly how until he contracts typhus while opening up a corpse in town. From here on the story is pervaded by a sense of fate, a sense that the ending has somehow already come and that we must simply wait and let things play themselves out.