Can you ask for some miles as a customer service gesture? It's a long shot, however, as the inconvenience is caused by a partner airline. Perhaps AS can convince the operating carrier to open business class space for you so that you have business class on every segment for business class miles.

I wouldn't cancel without first finding something (better) as an award ticket for the return. BTW, can you cancel just the return without needing new award space to be available for the outbound?

In the meantime, you could keep checking for business class award space to open.