According to the Sages, the Israelites did not believe that Aaron died until God was forced to prove that he had.

When Moses and Elazar descended from the mountain, the entire assembly gathered around them, and said to them: Where is Aaron? Moses and Elazar told them: He died. They said: How could the angel of death harm him? Aaron is a man who stood against the angel of death and stopped him by burning the incense, as it is written: “He stood between the dead and the living and the plague was stopped” (Numbers 17:13). If you bring Aaron to us, fine; if not, we will stone you. At that moment, Moses stood in prayer and said: Master of the Universe, clear us of suspicion. Immediately, the Holy One, Blessed be He, opened the cave and showed Aaron to the people. (Bemidbar Rabba 19)