In BG1 he was wrong. In ToB he's right.
No, he's wrong in both instances. ToB doesn't alter the fact that it's Bhaal's intention for the death of his children to cause his resurrection. It's the betrayal of Bhaal's high priestess that causes the god not to be reborn, and obviously Sarevok doesn't know anything about that. Had Mellissan remained loyal, Bhaal would have indeed been reborn through the actions of his children.
Does that have anything to do with it being a retcon?
Nowhere in BG1 does it say that Bhaal was aware of of Alaundo's prophecies, only that the god knew he would die during the Time of Troubles and tried to do something about it. BG1 doesn't say Bhaal intended for his children to wage war on one another, only that Alaundo foresaw that they would end up doing so. Nothing in BG1 contradicts the possibility that it was, in fact, Bhaal's intention for his children to be slaughtered soon after his death... but in D&D, even the intentions of gods do not neccessarily translate into actual future events.
After all, Alaundo's prophecies were what Alaundo thought would happen in the future, not what Bhaal thought would happen in the future. And before you say "bah that's more retcon nonsense" or whatever, consider this: a war, no matter how large scale, would not benefit a god of murder - it would benefit a god of war (i.e. Tempus). A massacre of children on the other hand...
Also, consider these Prophecies of Alaundo from BG1:
"During the days of the Avatars, the Lord of Murder will spawn a score of mortal progeny. These offspring will be aligned good and evil, but chaos will flow through them all. When the Beast's bastard children come of age, they will bring havoc to the lands of the Sword Coast. One of these children must rise above the rest and claim their father's legacy. This inheritor will shape the history of the Sword Coast for centuries to come......"
"The spawn of the Lord of Murder are fated to come into their inheritance through bloodshed and misery. It is the hope of their father that only one shall remain alive to inherit his legacy. I foresee that the children of Bhaal shall kill each other in a bloody massacre."
It would appear that in this case, a supposed ToB retcon (i.e. a Bhaalspawn replacing their father instead of causing his resurrection) actually fixes an inconistency within BG1
While it may have been Bhaal's intention for the massacre of his children to cause his resurrection, Alaundo knew the truth - that Bhaal would not be resurrected, rather one of his children would end up taking his place.
Of course the prophecies flag up another inconsistency in BG1 - if Bhaal spawned his progeny during the Time of Troubles, that would make Sarevok and the PC only 10 or 11 years old
! Seems the developers screwed up here - maybe someone got the idea that the ToT happened during 1348, rather than 1358? Who knows, but it seems ToB stuck with BG1's idea that the Bhaalspawn were sired during the Time of Troubles as well.
Obviously this is inconsistent with certain lore found elsewhere in ToB (and means the 35th level, father of Aerie's child PC in ToB would only be 12 years old!
), but then you can't fault ToB for this when the problem was inherited - this is perhaps an example of a time where there
should have been a retcon but wasn't!
Liking ToB's version better is one thing. Denying that it's a retcon is quite another.
Saying that there are retcons is one thing. Insisting that every tiny little, easily explainable detail is a retcon is quite another
.