Rumors About Evil Colleagues

My sister left. Before she left, she left her brother an article about what happened to her in the past year and asked him to help her publish it. My sister said that it all stemmed from a rumor in their company: as long as you have an intersection with colleague Z, you will either leave or die. From his sister's article, his brother learned the secret of his sister's company and understood his sister's decision, but are his sister's words really credible?