Actually, all he has to do to get released, is to do his time, and not assault someone, or take them hostage.He can't be kept in prison soley because of a perception that he's dangerously mentally ill :that might be a reason for placing him in a high security hospital.
Years of solitary confinement may well make it v difficult for him to be around other people : but if he commits ABH / GBH ( multiple) against other prisoners and guards, he's going to get charged. Many of these crimes have only added a year or two to his sentence.But there have been so many of them.
Taking people hostage, and threatening them- a civilian librarian, a deputy governor, a governor, a doctor, a lawyer, multiple inmates, and a education worker who Bronson credibly threatened to kill during the 44 hours he held him hostage, to name but some.
He presumably received psychiatric help during the 7 years he was sectioned in Broadmoor, Rampton ,etc.