Nanami is going to die, I suppose. It's difficult to see what other role she would play in the story. It would be a different thing if the farm slave period was longer and she actually played an important role in getting Yuuta to adapt into that world, but there was no such thing. Of course that as well wouldn't guarantee her life, but at least she would have another role. Now she's just a cute companion that appeared out of nowhere and isn't really doing anything other than following Yuuta around. That screams sacrifice for the sake of the MC's growth. Although, while I already abandoned the idea, there is still a slight chance she'd be used for betrayal. But I'm not expecting that at all. I reckon that wouldn't please the Japanese audience.