Heimdall's role is brief but consequential. He is watching, as he always is, until suddenly he is not. When Hela enters Ta Lo its hidden nature takes her beyond even his sight, and that absence is what he brings to Odin. He does not simply report that he has lost her. He also tells Odin about the Ten Rings, giving the All-Father the information he needs to draw the wrong conclusion entirely. Odin decides Wenwu must have killed his daughter, and from that single misreading an entire war unfolds.

Heimdall sets the machinery in motion and then steps back. He is loyal and thorough, and in being both he accidentally delivers the spark that sends Odin to Earth and puts him on a collision course with the very daughter he thought he had lost. The destruction that follows traces back directly to the report he gave in good faith.