With someone that is bipolar, what happens to them if they are not on meds for it?

Poor symptom control: If someone with bipolar disorder is not treated, there symptoms can become poorly controlled. Recurrent mood cyclic can adversely impact cognition over time.

See Kay Jamison: Unfortunately, uncontrolled bipolar disorder generally gets worse as a person ages. Not always, but very often, distinct depressive and manic phases merge into a so-called "mixed" state. This state has a very high risk of successful suicide. Naturally, some people with mild conditions or just good luck don't go that far, but it's not worth the risk. This is especially true as treatment works well.