AB 5063 is your existing flight with a different codeshare, so that's not happening either.

There is a reasonably priced flight out of Stuttgart that gets in at noon on BA, but that's not much better - it might buy you the window you need.

However BA is now selling tickets on the 709 ZRH-LHR so it may have been reinstated. Call and see if that might be the case.

The 720 is going out an hour late tonight but is running.

Just checked - 720 now showing as cancelled and tickets still available for the 709... No idea other than to turn up at the airport on time and plead your case.