Could you explain the concept of avatars merging into the 'unmanifest' as it relates to Sai Baba's departure?

The concept of merging into the unmanifest refers to a return to the source, the formless Supreme Brahman. Chapter 43 explains that saints are the 'personification of the form of Brahman' who incarnate for the welfare of people. Their physical form, like Baba's three-and-a-half-cubit body, is a temporary vessel for their task. When the task is over, they 'join their true form and merge into the unmanifest.' For Sai Baba, this meant transcending his material state to resume his all-pervading, timeless nature. He didn't cease to exist; rather, he became fully integrated with the conscious, formless reality from which he emerged, while still enjoying his true self and keeping his devotees 'awake.'