Whatever Peter III's original intentions towards poor Ivan, the question of what to do with him remained a hot issue politically. Not only did everyone know about his imprisonment despite Elizabeth's best efforts, but he had become a figurehead for various conservative factions across Russia. One of the first things Peter did on becoming Emperor was to ride to Schlusselberg prison to see Ivan himself. What he saw likely disturbed the new Emperor deeply.
While none of the guards who wrote about Ivan's condition knew anything about psychiatry, and they were likely encouraged to exaggerate his mental state to play up the perception that Ivan was insane, decades of solitary confinement can break anyone. Especially when you consider that he spent most of that imprisonment in a narrow cell without windows and with only candlelight that made him unable to tell day from night. What it did to a boy who had known nothing else since he was four years old seems ghastly to consider. One guard wrote that "In June  his fits became more violent: the patient shouted at the guards, quarreled with them, attempted to fight, twisted his mouth, and threatened to hit the officers.” Still, the treatment he received was inhumane as well and some guards teased him without mercy.
Not only was Ivan kept in solitude but the entire prison was closed to outsiders to keep out anyone who might try to free the young Emperor. In 1762, an unexpected coup led to the overthrow of Peter III by his German wife Sophie Friederike Auguste von Anhalt-Zerbst-Dornburg, a.k.a. Catherine the Great. After succeeding as Empress (and discreetly disposing of her husband), Catherine inherited the problem of what to do about poor Ivan who was still in captivity in Schlusselberg. One of the first thing Catherine did on taking the throne was to visit Ivan and issue new orders to his guards. Far more ruthless than her husband, Catherine made it quite clear that Ivan could never be allowed to leave the prison alive and that he should be killed if anyone tried to free him. She was likely the last woman Ivan ever saw.
Finally, what Catherine and all her predecessors had feared took place in 1764. A twenty-three-year-old lieutenant named Vasilii Mirovich learned about Ivan when he was assigned to be part of his outer guard. Disgruntled over his lack of promotion, Mirovich came up with a scheme to free Ivan and take him to St Petersburg to overthrow Catherine. While there was no possibility that the long-imprisoned Ivan could ever rule Russia considering his mental state, Mirovich and his supporters likely saw him as a useful figurehead.
On July 4, Mirovich deployed the soldiers under his command and arrested the commandant of the prison. He then positioned his troops to storm the barracks where "Grigorii" was being held. And it might have succeeded if not for Catherine's standing order of what to do with Ivan if anyone tried to release him. Ivan's jailers, terrified for their lives (and what Catherine would do to them if he left the prison alive) promptly rushed into their prisoner's cell. Ivan had already been awakened by the sound of gunfire but he suddenly began fighting for his life when he realized that the guards were there to kill him. Despite his resistance, the guards quickly stabbed Ivan to death with their swords and Mirovich burst into the cell just seconds later. Ivan's death put an end to Mirovich's ambitious schemes. He promptly surrendered to the prison commandant knowing that he would pay with his life.
The real question though was what to do with the guards who had killed Ivan. Considering they had been following Catherine's orders, she had no problem clearing them of any blame. If anything, they were heroes for ending Mirovich's plot by sacrificing the life of one man who, as Catherine's own manifesto would state, was "unfortunately born." After several days, Ivan's body was buried in an unmarked grave somewhere in the prison courtyard.
As for the rest of poor Ivan's family, they fared little better. By the time of Ivan's death, his father, Anton Ulrich, had been imprisoned for twenty-two years along with his other four children. While the house where they were kept was slightly less bleak than Schlusselberg, everyone was still confined to two rooms (the men in one room and the women in another). Prince Anton eventually went blind in captivity and died in 1776, having outlived his eldest son by thirteen years. His body was taken out and buried in secret, much as Ivan had.
After another four years of imprisonment, Catherine eventually relented and allowed all of Ivan's siblings to live with their aunt in Denmark. By this time, they were all in poor health and had mainly learned to read and write on their own (Elizabeth had not permitted them any formal education). The oldest daughter, Catherine, was completely deaf while the others suffered from a range of other maladies. The prospect of being around other people terrified them but they were eventually led out of the prison for the first time in their lives and placed on a freighter for the last part of their journey.
It wasn't a particularly happy existence for them though. Their aunt, who happened to be Denmark's queen, only took care of them out of duty and never bothered to visit. Since they only knew Russian, they had trouble communicating with the servants who often took advantage of them. Still completely isolated from Danish society, they slowly died out, one after another. Ironically, the eldest, Catherine, was the last to die, deaf and alone in a strange land. In 1803, she wrote a plaintive letter to the then-Emperor Alexander asking to be allowed to return to Russia. Despite her poor writing skills (she had been largely self-taught), Catherine managed to convey her horror at living in Denmark surrounded by servants who openly mocked and stole from her. After years of being ignored, Catherine finally died, forgotten and alone, in 1807.
Catherine's death is a sad footnote to the tragic life of the man who might have been Emperor Ivan VI of Russia and his siblings. Would history have been changed if Ivan had remained on the throne? Undoubtedly. Still, the story of Ivan and his family is a tragic example of the kind of cruelty that can result from sheer political necessity. While Schlusselberg prison s now a tourist attraction for its historical value, the exact location of Ivan's grave is completely unknown. Countless tourists have likely walked right over his grave site without any idea of where they were stepping.
A sad fate for an Emperor.