Since it sounds like your AP is already activated, I'm pretty sure the answer is no. Once activated, it is good for one year, regardless of whether it is used or not. The only change you can make is to upgrade it to a PAP and it will still expire on the same day. If you can't get back before it expires, I'm afraid you are just out of luck.
If you had an unactivated AP voucher, you might be able to trade it for MYW tickets.
I'm sorry you had to cut your trip short.