Disney released some new information regarding annual passholders in their updated travel and information page. The main changes are that if you have already paid your pass in FULL then you will get an extension of your expiration date by however many days the parks are closed. If you do not want an extension you can request a partial refund on however many months you still have left to go on your pass.
If you are doing the MONTHLY PAYMENT PLAN then:
Monthly payments will be waived for the length of the closure.
Payments made between March 14th through April 4th will be refunded.
You will not get an automatic extension on your pass.
You may choose to extend their pass the length of the closure and pay the amount at a later date.
The full statement released by Disney is below: