After giving this some though, I can’t say. I’m thinking that what you’ll need is create an acf/save_post action with a priority of 20 so it runs after the acf save. http://www.advancedcustomfields.com/resources/acfsave_post/. The reason being that since the field is hidden with conditional logic and not submitted that update field action for the field will never be called, so you can’t go that route.
In the save post hook you need to get the conditional field and test it then delete delete the content of the other fields depending on that value. You’ll need to remove the values from the acf field as well as deleting the post terms, I think.
