Is it possible that you could be sent to a long term mental hospital permanently? what would need to happen for this?

It's possible: Over the past 30 yrs or so, there has been a push for deinstitutionalization of the chronically mentally ill in the U.S. Nowadays, If someone is sent to a psychiatric facility long term, it is most likely b/c the persons were involved in repeated, serious attempts to injure themselves or others. Forensic psychiatric hospitals evaluate and treat mentally ill offenders who have committed crimes.