I think the OP deserves more of an explanation as to why, whether it'd be written or in-person, but I'm not sure if there is a requirement to provide one (especially in 5-10 sessions).

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I do question if extra sessions for closure would even be helpful for you or would it just add to the pain. I assume if he is forced to provide closure sessions by a board it wouldn't be the same warm, caring demeanor that you recall over the last 6 years. It would be formal and I'd imagine an emotionally detached style because of the annoyance of having to provide these sessions. Are you prepared for that scenario if the closure sessions are granted by his professional board??

What does it closure mean to you? Is it figuring out what happened? Do you just want to review your work together in person? Is it wanting him to reconsider? Or is it just being able to say goodbye? Will the closure sessions resolve anything? Or will it just make the wound bigger and deeper?

Being able to answer those questions will tell you whether it is in your best long-term interest to fight for closure sessions OR whether you should just file a complaint while finding ways to cope with the abandonment.

It's not fair that you had to go through this, but given that you have--what do you personally gain from spending all your time and energy on a complaint that may drag on for months. Finding out what you can do for you, while compartmentalizing the complaint, is critical. Again, it's not fair, but where can you go from here that leads to self-growth?