A Microsoft file hosting and synchronization service.
It’s important to understand that Microsoft does not have the authority to manage individual users within an organization. Each organization’s IT department is responsible for managing its own users, following its own protocols and security policies. Microsoft’s role is to support the organization’s IT administrators by providing tools—not to bypass them or intervene directly.
Imagine a situation where a disgruntled former employee—or student—gets fired or removed and then contacts Microsoft to regain access to sensitive internal data, or to impersonate as someone representing the organization by using the organization's email address. If Microsoft were to help them directly without the organization’s knowledge or approval, it would be a major breach of privacy and security. That’s why Microsoft strictly defers to the organization’s IT department for any user account matters.
I am sorry, you do need the school's blessing to reinstate the email. If they say no, it is NOT Microsoft's place to override that decision.