Initially the player may just be staving off imminent disaster as Cyric and his friends move quickly against the player - several strong deities against a relatively weak one. I could imagine the player being forced to abandon the Throne of Bhaal and going on the run across the planes. The player's goal would be to gain followers (faith=power), usurp the divine portfolio of another god, and carve out a base of power in the wider multiverse.
…….It had been about 10 years since the BG games, which may have been too long for a direct sequel. I know we were planning a reboot of the series that could appeal to gamers unfamiliar with the franchise.