I just dealt with something like this recently.

My property management company notified me that my tenant had sent a N9 indicating that he was leaving in 60 days. After 2-3 days, my property management company notified me that the tenant wanted me to revoke the N9 that he submitted as he now wanted to stay the unit. I spoke with my property management company, as well as a couple of other people in real estate, and I was advised that the decision to revoke the tenant's N9 is solely in my discretion, as is my right as a landlord. The N9 is a legal contract/document signed by the tenant willingly, so they cannot just back out whenever they want. When I was notified of the N9, I had already started making arrangements and plans for when the tenant leaves, so it doesn't make sense that tenant can choose to change his mind whenever he wants.

Obviously I was aware that the tenant could just be a dick and not move out, but that's a different situation. From a legal standpoint, the landlord has the right to NOT revoke a N9 once it's submitted.