I was also able to change destination (within 300miles) after my original award flight was cancelled. I simply stated that my understanding was that I could switch to an alternate airport that was within 300 miles and rebook on a flight that was similar to the original schedule. In my case the closest alternate flight was about 2 hours different from the original, and about 120 miles away. The agent had no issues making the change and did not need award availability on the new flights.