In these times I would value a direct flight above almost all else. There is no predicting what could happen by the end of 2020, Christmas travel plans have been disrupted at very short notice by border closures. I think most European governments will be very jumpy about “importing” new variants of C-19 and borders will open and close repeatedly.
If MAS does go under, or cancel their LON route your ticket is issued by BA, so they will be the first port of call for a re-routing, personally I would look on MAS as an adventure you would not otherwise have had. You have a a flat-bed on an A350 and a direct service, how bad can it be?