To answer my own question (halfway), here is the answer I received from Disney (bold is mine):
"Annual passes that were paid in full at the time of purchase are going to be extended out by the length of time that the closure period meant you weren't able to visit (in your case, March 16th to May 10th), once the parks reopen. We currently don't know when exactly admission will resume for annual passholders who expired during the closure period. For example, everyone who has an extension due may begin that extension on July 11th, or they may be staggered - we do not have that information yet. I bring it up just to highlight the fact that it has not been announced for sure that it will begin on July 11th!"
Me:
Okay, so we may not be "active" when the parks first reopen, but the specifics haven't been decided yet?
Them: "That is correct! Your extension very well may begin the day the Theme Parks begin to reopen on July 11th, because it hasn't been established that it won't be, it just hasn't been established that it will be, either! I don't mean to sound daunting, but just want to highlight that there has not been a decision made either way."