FlyerTalk Evangelist and Ambassador: The British Airways Club
Join Date: Jun 2008
Location: Somewhere between 0 and 13,000 metres high
Programs: AF/KL Life Plat, BA GGL+GfL, ALL Diam, Hilton Diam, Marriott Gold, blablablah, etc
Posts: 33,194
Very sorry for your loss.
My experience of BA Holidays is that changing departure country is always very tricky so I doubt that will happen; London might or might not be allowed but is a lot more likely though it may indeed incur additional costs. My suspicion is that they will likely not allow a free cancellation either.
They will probably allow you to move the trip to different dates however or simply shorten it (with the same origin) - which is what would have been allowed on a straight BA ticket too (to my knowledge, not cancellation of change of origin) but you can only call and ask.