I have a question for you. What is the golden rule of time travel? The answer is DON’T CHANGE ANYTHING! Now here’s another question. Does any main character in a time travel story follow that rule? NO, and this is no exception.
While at first shocked at the fact they are 11 years in the past, they don’t need to worry about their way back. As long as Shinobu can suck Araragi’s blood, she can have enough power to travel back to present time. So seeing that their escape route is guaranteed, Araragi decides on what to do while they’re still in this timeline. But first, he needs to drag Shinobu away from his younger self.
So what do they end up doing? Try to change time of course! The time period he’s in is exactly the same year Hachikuji got killed in an accident and became the lost snail oddity. Initially he wanted to prevent everyone’s problems to prevent all oddities, but the rest of Araragi’s harem deal with issues that are too personal for an outsider to change. Like Oshino said, these issues have to be solved by the victim itself.
Hachikuji, on the other hand, became an oddity through an accident, so it’s easily preventable. On their search for her, they come across a loli-Hanekawa(who obviously gets the Araragi molestation treatment), a hyperactive policewoman, and even Hachikuji’s father who tells them that Hachikujis ran away from home. We know that both her parents were divorced, and the reason she became an oddity is that she got lost on her way to her mother on mother’s day.
Thankfully they do find Hachikuji in the same park we saw her at in Bakemonogatari. And how does Araragi prevent her from getting killed? Chase her around like a Molester of course! To be fair it does work, and Araragi is fully aware that what he’s done means that she won’t be an oddity, thus never meeting her in the new timeline. But Araragi really shouldn’t have underestimated time, because the ep ends with him hinting at the apocalypse(sheesh, saving a lost loli will destroy the world? Or was it molesting Hanekawa?).