The way I see it is this:

Fae are spirits of nature and so are tied to nature. They go through a "rebirth" just like other parts of nature would. They just go back through the cycle of life.

Aspects, Avatars, and Spirits in general go through this same process as well, unless their essence itself is destroyed like Sun's.

Angels and Demons I don't know about. They could just die and the cosmic plane might just raise another, or their essence might return to the cosmic plane.

The Demon Lords and Supernals are a lot different. They're tied to their respective planes and are so much a part of them that they really never leave, even when their bodies are taken away.

Divine and Ephemerals...I dunno. Ask Estarra.

I wonder now if only PC's step through the Portal. NPC's that are normal races still have shards within them, just not awakened and should die permanently, as in the histories it quite clearly shows that when people died they were gone for good (hence the incredible despair surrounding Spirit Sun). Somewhere along the line, that changed. Some NPC's are important enough to keep around even if they haven't apparently stepped through the Portal. Or have they?

I suspect they're not roughly humanoid enough. It would bork up the emotes and clothes and stuff like that. 1 head, 2 arms (though more might be ok if they did nothing) and 2 legs. I'm pretty sure that's it.

I have always thought that named NPCs always come back... because it simply is not their time. It is not the fate of "insert named NPC here" to die at the hands of "insert PC here". Those who come back have something left undone. At least in the eyes of the fates. That was what I thought at least.

But that would mean guild tutors haven't gone through the portal of fate?

Certainly the bard guild tutors haven't!

I've heard Master Eurytus speak on the GT aether, so that might imply that he indeed has passed through the Portal, as only members who have done so can speak on that aether. But then again, so can the Elders, and they haven't passed through the Portal, have they?

Nope. Also, it's possible for fae / angels / demons / Avatars / Supernals / etc. to speak on the GT aethers, as well as the Bard guild tutors (who are the voices of Elder Gods).

The ebonguard guild tutor most certainly did not pas through hte portal of fate.

Good point.

I personally atribute the respawning of named mobs to an equvilent of city conglutination.