Did Sai Baba ever say he would return after leaving his body? If so, in what form?

Yes, devotees held onto the full confidence that he would return. According to Chapter 43, Maharaj had explicitly told his followers before he left that he would "appear again" as an "eight-year-old child." This promise is considered the sacred word of a saint and not to be dismissed. The text even compares this to the Krishna avatar's appearance. The purpose of this foretold return is for the salvation of his poor and devoted followers, giving them a strong reason to maintain their faith and not fall into doubt.