Simliar situation to me my return from LAS (LAS-JFK-LHR-AMS-LHR) started with a 7:55am flight from LAS to JFK, that was cancelled, no notification I just happened to take a look at my booking to see what seat I had on one of the legs. I was automatically rebooked on to the 12:12, but the rest of my itinarary hadn't been changed so spent hours of faffing to eventually get on the last flight of JFK (BA182). As a consequence I'm probably have to ditch the last LHR-AMS-LRH return leg as otherwise I'll be travelling for nearly 24 hours and also t'other half will murder me for not being home! First time I've ever dropped an ex-EU leg

I booked mine through a TA, they were extremely helpful in sorting out the rebooking to maintain the hop via JFK. I'd call BA Hols and ask if they could reroute you how you want - don't ask don't get etc.