In that case I would expect the refund to be the number of days from when the parks closed to the day your AP is scheduled to expire.
Under any reasonable interpretation of contracts - the refund would be based on time alone and not usage. If they attempt to claw back based on days that would be beyond ridiculous. Just think of the many cases where an AP holder went 10 random days during the first 4 months of the AP before closure. Disney can't just say "well - you got the value out the AP already so no refund" at all. It would make zero sense. That's not to say they can't just change the policy but as currently stated, the cancel option would only be logically interpreted based on time.