It depends what sort of failed suicide you're going with. Generally, you only need a mature filter for nudity, sex and violence. Suicide or the aftermath, don't actually require it unless you intend to show violence or gore with it or show it graphically, which is generally advised against anyway. However, it's generally considered good form that if you're going to deal with issues like suicide, you have some kind of content warning at the start of the story or chapter. That way people know that it's coming and can decide if they want to continue or not.
