BA leaving Gatwick would be great news for me so, selfishly, I hope it happens. It also, I'd have thought, makes sense for BA through consolidating London operations in one base (though with some risk of having all their eggs in one basket). They haven't done it before because BA doesn't have enough slots at Heathrow to service all its routes (and buying new slots is difficult - pre-virus they were rarely sold, very expensive and some limits were imposed to stop BA monopolising routes). But, presumably, BA will be running many fewer services overall anyway for a while and rival Heathrow airlines might disappear entirely (Virgin?), or at least scale-back (especially if Airline X can get some desperately needed cash by selling a Heathrow slot pair). So - if BA itself still has any money left after all this - there is an opportunity for it to at least consider buying up new slots (at a discount price, perhaps), and consolidating.
At the very least, again being self-serving, I hope they transfer the Seville flight to Heathrow when things start up again!