Teenager Wants to Leave

We live in Michigan and adopted our two children in IL in 2010. Our 13-yr-old son is currently in a short-term inpatient psychiatric hospital because he is a diagnosed pyromaniac with conduct disorder, lack of remorse and empathy, and a desire to kill my husband and 12-yr-old daughter. We have always had some attachment issues, and he’s always lacked empathy, remorse, and impulse control. It has worsened in recent years, and we admitted him two weeks ago when he set a dangerous gasoline fire in our barn and told an adult family friend that he wants to kill us so he doesn’t have to be forced to live in our family anymore. The question is: does he have to? Is he able to voluntarily make himself a ward if the State or dissolve the adoption? We’re wondering, if he knows he has the choice to either stay in our family or leave, then maybe he won’t be as resentful, because staying is his choice, not something “forced” on him. And if he chooses to leave, then we won’t have to worry about him killing his sister or burning us all to death in our beds with a contraband lighter.