Just had an August 2022 BA avios booking LHR-HND in J cancelled. Called up and managed to get through to BA quicker than usual. However, it seems BA are not offering re-booking onto JAL as these are no longer codeshare flights (and was told this is the same regardless of whether flights were paid with cash or avios). I was offered Finnair via HEL but availability was limited. It may be worth someone updating the wiki on this thread (I don’t have sufficient posts to do so).