Why does Ishi choose to return to the museum rather than stay in the Yahi world?

Ishi has many reasons for returning to the museum rather than staying in the Yahi world. First, He says that the Yahi world may not be dead for him and Majapa, but it is dead in the canyons and hills. These physical places are no longer the world of the Yahi. Secondly, he knows that he still has a lot of work left to do in order to finish his work to preserve the Yahi Way. He has more artifacts to create and more information to record in the notebooks. Ishi wants to return to the museum because he cares about Maliwal and Majapa. Ishi wants to ensure that Maliwal does not stray from the Way and continues to live wisely. As for Majapa, Ishi is concerned about the possibility that he may have to go to war. He wants to be nearby so that he can offer prayers and sacrifices for Majapa's safe return.