Does selective mutism usually go away after awhile on its own in children?

Yes. Selective mutism is a form of social phobia or anxiety. Treatment is usually successful, and the children often outgrow it as they become more self confident in social situations.
Yes - After Awhile. Selective mutism is usually related to anxiety for some reason. It tends to improve with time. However, it may last for a long time, which leads to frustration for parents and adults around the child. Treatment of underlying anxiety is usually helpful.