I just recently had to change plans and travel at short notice. The only tickets available were full fare Y because the return date (on which I had no flexibility at all) had very little availability, and the new outbound flight I needed to take was only 5 days from booking.
So I bought a one way ticket on another airline and redeemed miles on AA one-way in Y for the return at Anytime rates. No, it wasn't ideal, but 60k miles per ticket in question seemed better than $3k.
I thought of using miles to travel in J, but the relatively short flight didn't seem worth the 100k per person rather than 60k, especially since on this journey we weren't going to be able to enjoy the food and drinks in J. (And in any case, redeeming 100k AA miles for a roundtrip BA flight in F for LHR-CPT seems much more worthwhile than using them from a one-way transatlantic on AA in J.)
The only benefit was that I topped up another of my mileage accounts using the other airline (frustrating though the experience of not travelling on AA was).