The 380 is currently listed in the schedule for all of October up to and including Sat 26 October (the last day of the northern summer 2019 scheduling season). It is common to find aircraft allocations changing when the season changes, so this is not an unexpected thing to see.

But that, I'm afraid, is as much proof as you're going to get from public sources.

Aircraft allocations are always subject to change, and we are probably not yet in schedule change season for northern summer 2019. Between now and the end of February, you can expect BA to tinker with and finalise the schedules for that season, and there is therefore always a possibility this far out that any aircraft including the 380 could yet be redeployed elsewhere.

If you want advance warning, inside information in the form of gossip and rumour is likely to be the best you'll get. But by definition, it will not be hard proof.