How was Sai Baba's departure from his physical body described? Was it considered a normal death?

No, his departure was not described as a normal death. Chapter 43 explains it as a voluntary and controlled process befitting a great Yogi. It states that Sai Samarth could "die at will" and that he consciously "burned the body in the fire of Yoga." This act is presented as him merging himself back into the unmanifest state from which he came. The text dismisses the notion of a conventional death for saints, comparing it to an eclipse, which is merely a "defect of vision." His leaving the body was the completion of his task, after which he simply rejoined his true, formless self.