But since the laws of your country probably don't allow your son to skip school and enroll at MIT right away – or, as Steven Gubkin pointed out in his comment above, your son might overestimate his own abilities –, you still need a strategy. If your son is not willing to see a psychologist (which I can understand), find one yourself or find whatever organization there is to help giften children in your area (or nationwide) and contact them and go there alone. Your son is not the first of his kind, and these people will have some practical ideas for the next steps you and your son can take. (If you chose to see a psychologist, don't visit some random psychologist. Call them and ask who they would recommend in your situation. Or contact your local university's psychology department.)
There are programs for giften children to visit university while still going to school, or there are special schools or after school activities, and these organizations will know the steps for you to take to get your son to where he will flourish. For you and your son to understand which of the many possible options are best, a psychological assessment will be necessary. You can explain to your son that this does not mean that anyone will want to push him from the path he envisions for himself, but to help him find the best approach to get on that path. Many professionals make use of tests to understand themselves better and better be able to manage themselves.
But he is still nine, emotionally, so you need to be the mother and nudge him a bit, if he is afraid or disinterested.
Note: Schizophrenia is related to high intelligence. For example, the twin of a highly intelligent person has schizophrenia more often than that of persons of average intelligence, and vice versa. The fate of your husband, who probably was highly intelligent as well, makes it important that you also consider the medical and psychiatric implications of high intelligence. Don't force your son, but his unwillingness does not mean that you should go through this alone.