Answer:
Miep chooses to leave the building because he knew that there was a chance he/she would never come out again.
Step-by-step explanation:
Based on the clues from this passage, Miep thinks back to when he heard people who enter the building do not always come out again. I used this information to conclude that he leaves the building for his/her own safety.
*I put his/her and he/she because I do not know whether Miep is a girl or a boy.*