Flying Delta for an international r/t, BOS-LHR on 3/17 and then LHR-BOS on 4/6, was a sale fare back in OCT, didn't see deals out of ATL (home). Yesterday wife and I got the schedule change e-mail, pushing back our return 4 hours 20 minutes (which is on Virgin Atlantic), which won't work for us as we need to get back to ATL that night (On Southwest with points and companion pass)

Do we have a chance of getting on LHR-ATL instead if we ask? Or, LHR-ATL-BOS (and getting off at ATL)? Does it help our chances that these 2 options are on Delta and not Virgin Atlantic? What tact should we take?

Do we go crazy and ask for ATL-LHR r/t?

Thanks!