The users added into a community via audiences cannot unfollow or leave the community.
In the detail page of the community, a message will appear when the user tries to leave or unfollow the community.
This feature implies a new notification when the user is added via audience (even if the user was there before), but not when the user is removed.
The notification will redirect the user to the community detail page.
If you want to know more about this feature on the web check this out.