My annual pass expired March 30th as well.
I called to see if my expiration date would stay the same (refund), reset to whenever they re-open again, or if it would reset to December (my next trip). The call was long, and I talked with at least 3 cast members. Long story short, they recommended I wait until a further email or website post explains what can be done. This is because my certificate hasn't been activated yet, so the refund would only apply to my pass that expired in March. They were not sure how the certificate would apply or if it could be partially refunded as well.
Basically, just wait longer was the answer. I hope this saves a very long phone call.
If I'm right in remembering that they closed on the 16th, then you basically have 14 days left on your AP. So, you can either apply for a refund, in which case they'll pay you back for those unused 14 days, or you can take the extension, which means that you'll have 14 days to use when park re-opens. If you take the extension, then your new renewal anniversary would be 14 days after the parks reopen then. So, if they open on the June 1st, your new renewal date would be June 14th. Going forward, you'll be paying the renewal rate for June 14th to June 14th, if you go this way.
Since the scenario is unprecedented, I don't know what they would do about your renewal, if you wanted to take the refund. If you take the refund, you'll be refunded for the 14 days before your pass expired, then either of these might happen:
1) They renew you with the March 30th date, and you pay full price for the renewal.
2) They renew you with the March 30th date, and you get a refund on that AP as well, for the number of days between March 30th and park open date.
3) The renew you on the Park opening day, and that is your new renewal date going forward.
4) They consider you as non-renewed, and you start a new AP on the day of your Dec trip, apply what you already applied to the renewal towards the new AP, and you're responsible to pay the difference.
5) They consider you as non-renewed, and you start a new AP on the day of your Dec trip, apply what you already applied to the renewal towards the new AP, and they don't make you pay the difference.
Considering you were looking to do a renewal anyways, I'd recommend you just take the extension, as the safer bet. The only thing the refund seems to guarantee for you would be to get back 14/366th of your AP fee, which at the current price of $1272.68 works out to $48.17 (though probably less, as that's based on the current price, not the price you paid a year ago).