A meta response could be 'whatever works best to advance the story and is compelling for as many players as possible.'
The GM gets to decide if Pharasma had already decided that this high priest was on his way out, or scheduled for many more years of life. If she *really* wants him to return, she'll send another priest (or outsider servant) to raise or ressurect him. Or the slain high priest might return as an actual outsider servant of the goddess, being all 'if you strike me down, I shall become more powerful than ever!'
Or, the cleric's *wife* might return as a psychopomp or other outsider servant of Pharasma, and urge him to step away from this path. Maybe it was her fate (or their child's!) to become a psychopomp at this time, and their mortal deaths were a necessary step in their ascension. Maybe it had to be a child, reaped before they made their mark on the world (and became 'too enmired in worldly concerns') because this particular intended servant of Pharasma deals with lost possibilities and potential cut short or higher more esoteric spiritual matters that require a certain distance from concerns of the flesh or whatever.
But, for the most part, a god can't get up and deal with it personally every time one of her clerics dies. PC clerics die all the time, and the closest thing to divine intervention is the GM saying 'roll up a new character.' Why should NPCs get all the divine intervention?
The church, on the other hand, may indeed send an Inquisitor (and his or her goon squad) to investigate and mete out appropriate punishment, leading to a potentially fun encounter, later. (Note that Pharasma is very much not a *good* goddess, or even a lawful one, so killing off a bunch of her flunkies who attacked your party first, even if they were trying to avenge the killing of a priest of their faith, isn't going to cause anyone alignment issues, except for the dude responsible for this 'misunderstanding.' Indeed, there's a one in three-ish chance that the Inquisitor sent might be evil anyway!)
As for the 'new boss,' note that gods don't *have* to agree to take on a fallen cleric of some other god. The evil god might have half a brain in it's outsider skull and think, "Yanno who would make a terrible person to make a cleric and give all sorts of power to? Someone who just screwed over their last god..."
On the other hand, some gods might be recruiting, and Norgorber might find his red-handed murder, and the deadly deception that preceded it, amusing and golf-clap-worthy, while Zyphus, more intrigued by 'humorous' Rube Goldberg-style 'accidents' (like something out of Dead Like Me or a Final Destination movie) might find this a tawdry tableau of madness-in-grief and unworthy of his favor. Too hot. Too 'in the moment.' Not enough planning and scheming and setting up a plausibly-deniable 'accident.' Not cold enough. A proper paean to Zyphus would have started with arranging 'accidents' for the High Priest's family, preferably ironic or symbolically significant ones, such as drowning someone (reversing Pharasma's traditional association with baptism as rebirth) or arranging for the statue of Pharasma to topple over and crush someone (easily misinterpreted after-the-fact, perhaps by the evil-doer himself, as a sign of divine disfavor!).