If IAG want the slots, they will have to take most, if not all, of the fleet, otherwise they will loose the slots, they will need a lot of BD's current people too, to fly these aircraft. The route network will be pared an optimised over time, probably domestic and other competing destinations first.
The A32X's are fairly compatible with the rest of the BA fleet, so it's not a huge deal, Im sure Ba can find a use for most of the BD fleet. I suspect the A330s will be disposed of pretty quickly, if they are acquired at all, those routes would simply be operated by 767 or 777, I should imagine.