Waited a week. Saw that I could still book my original BA codeshare flights on aa.com BUD-LHR-AUS so I called. Was told AA canceled the BUD-LHR flt. I said it was a codeshare with BA that is still operating and she said it was an AA operated flt. Put me on hold and later told me she was able to get me on a BA flight still in J. Not sure why reservation got messed up but we are in special times. I hope by making this change I'll still be eligible for a refund later if it doesn't feel safe to go (May 13-23)
So my itinerary change wasn't caused by an upcoming flt cancellation (as of yet). Not sure why I didn't get rebooked onto the same flt automatically.