On past performance BA would certainly want a consistent longhaul product, which would imply a 767 or 777. Ideally they would probably want an aircraft with more cargo capacity than an A321 can offer.
It seems unlikely they have sufficient spare longhaul aircraft to replace the 320/321 on these routes and the plan appears to be that the 332s will be disposed of soon. But if they discontinue them there will be more uncovered slots to protect at LHR. Why close them unless the economic performance is shown to be unacceptable ?
There would seem to be a case for continuing them to see how they can perform under BA ownership. The A321 seems to be a good size in terms of passenger numbers, and BA will presumably make the decision whether or not to accept its limitations in the short to medium term.
LHR-FRU I believe started life as a BMed contract with a Canadian mining company. Does anyone know if those mining contracts still sustain the route ?