[Bishop Edward]

Well since you asked... I've always thought it was something like "Cyric wins (apparently), Leira dies (apparently)" I also see Ao's granting him the domains as legit, but that doesn't mean Leria lost them or Ao took them from her...

The way I see it, there can be two deities with claim and power over the same domain at a time... Although perhaps by doing so, they split the portfolio into sub portfolios (like what happened when Tyche, god of luck, was split by Moander into Tymora and Bashaba, forming a goodess of good luck and a goddess of bad luck). Ao tries to keep it from happening, and usually it doesn't/can't, but it could have been possible here due to Leira's deception... (if we're going with subportfolios, Cyric would have taken Lies but Liera kept Illusion proper, breaking up the greater Deception domain).

thus Cyric did become the Prince of Lies (which eventually lead to his writing the Cyrinshaad, reading it, and going insane after believing it himself), *and* Leira managed to hold on to *most* of her power, and took on the fullest form of her ideals of deception and illusion by faking her death, and continuing to operate as a deity on her own merit...