Can manic depression with psychopathic tendencies just go away?

Yes and no: Not sure what you mean by psychopathic tendencies, but manic depression usually has periods of stable mood between episodes of mania and depression.

Bipolar Disorder: (AKA Manic Depression) is usually a life-long condition. However, there may be periods of normalcy and with treatment symptoms may come under good control. Regarding psychopathic traits - leopards don't usually change their spots (unless they are highly motivated to do so).