Taken from a forum post by GM Armifer.

As most of you know, one of the key features of the Necromancers is that past a certain point in development, they are forsaken by the gods and must seek refuge in other forms of immortality. Here's how it'll play out.

Unsullied (newbie, pre-damnation) and Redeemed necromancers gain favors and can depart like every other player in the game. An unsullied necromancer might have enough Divine Outrage to prohibit Clerics from successfully using their corpse-assisting spells on the Necromancer, but even then they retain full use of depart and favors. Redeemed never have any problems here.

Forsaken Necromancers lose all their favors upon their damnation and... never get any more. The secret of the necro favor is that there is no such thing as a necro favor. Instead, they can have access to up to three options.

1: They may do a favorless depart like everybody else. This lands them in the exact same spot and with the exact same penalties as anyone else that departed there with 0 favors.

2: They may depart guild. This is almost exactly like the favorless depart, except that the destination is the Necromancer guildhall. Useful if you can't be seen at a nearby shrine, just bear in mind the complications you're setting up for yourself if your grave happens to be on Mer'kresh.

In #1 and #2, the messaging is different for forsaken Necromancers, reflecting the intervention of a "patron" which protects their soul from judgment long enough to reincarnate.

3: With knowledge of the 4th tier, transcendental metaspell "Spiteful Rebirth," they may depart death to resuscitate themselves. This temporarily cripples the Necromancer with a potent version of Death's Sting and brings him back at the very brink of life, but it allows him to remain in full control of his possessions and location.

There are limits to how often a living necromancer can depart death: there's a hard limit per 24 hour period based on his spirit health and Stamina, and a short-term limit that he cannot use it again while still laboring under the Death's Sting from a previous death.