I'm not sure when your booking is for, but looking at a random date in October the BA1416 still exists but has been pushed back in the timetable to 14.30pm. The earlier BA1414 which used to leave leave LHR first thing in the morning has been pushed back to 9.45am.
Have you checked on the BA website to see if there are any flights running on the day that you need that are better timed for you, and if so contacting BA to see if they will move you. The other alternative might be to see if there is a better timed flight from Heathrow to Dublin that they would move you to. Not great having a two hour journey on a bus to get back to Belfast, but might be preferable to 12 hours in Heathrow.
Thank you for taking the time the reply.
The flight is for a Tuesday in December and I did check the BA website and there are only two flights to Belfast that day, BA 1414 at 6 45am and BA1422 at 18 45pm.
I can see other options on other days. I was considering changing to Dublin .
These flights were to return home from a Cruise, which has now been cancelled, so I am hoping BA actually cancel the flight from Buenos Aires and I can then rebook for next year as we have moved the cruise to next year.