Yeah, it's pretty heavily foreshadowed at this point. The Symbol of the absolute is literally their three symbols combined into one. Their lieutennants/chosen are 'an immortal necromancer' (representing Myrkul) a would-be Tyrant (Bane) and a psycho murder-assassin type (Bhaal). Furthermore, all three got cards in the mtg tie-in set, despite only Bhaal being particularly relevant to the events of BG I+II.... which would mean their inclusion is relevant to BG III.
Oh yeah, and that thing about them being conveniently demoted to conveniently-in-the-realm-of-plausibly-killable 'quasi-divine' status. Veeery convenient.
