It would be rather weird to make a big song and dance about bringing Bhaal and Myrkul back just to kill them again IMO. Still, I fully expect this to be the case in BGIII. Why else all this convenient stuff about 'Well, they are technically mortal 'quasi-divine beings and not full gods, even Bane, for some reason'. Larian/WoTC setting them up to be killed is a real possibility.