I just got off the phone with V.I.PASSHOLDER Support and I thought I'd pass on her answers to my question. It may save someone else an hour of waiting on the phone.

Q: We bought our passes beginning of February and the parks closed mid-March. Will we get refunded for 10 1/2 months?
A: Yes

Q: How will the Premier Passport be handled?
A: Since Disneyland is opening later than WDW, the cancellation (or extension if we decide not to cancel) will be handled by the Disneyland Annual Passport Member Services. So if you want to cancel a Premier pass, you may want to try calling Disneyland first.

Q: Can we cancel just the WDW part, and keep the Disneyland part?
A: No. It's all or nothing.

Q: Is there a deadline to decide?
A: No deadline.

I hope this is helpful.