Excommunication

In standard D&D, Clerics receive their spells from a patron deity or, in some less common cases, from a force, philosophy or similar agency. One consequence of this is that should a Cleric fall away from their patron (generally by shifting to an incompatible alignment) the Cleric will lose all access to spells and powers.

(In some older versions of the game, the DM was actually encouraged to keep an eye on the spells the player of the Cleric chose to prepare, and potentially to substitute some or all of these for spells of his own liking.)

I'm not really a fan of this notion, partly because of the interference with player agency, partly because I simply don't want to use alignment, but mostly because I would prefer my religions less monolithic than that implies (since it's hard to have a heresy when the deity is giving a clear and immediate guide to his intent).

For that reason, in Terafa Clerics will not be granted their spells and powers by their deities directly. Instead, those powers will be granted by some unknown and unknowable Source. The Cleric taps into that Source in the name of the deity and is granted spells. And, as a consequence of this, it is impossible for the deity to interfere with the granting of spells - the Cleric's player chooses his spells, and that's that, and also the Cleric can't fall away from the deity by changing alignment or similar (of course, the Cleric could fall away from the church and suffer all manner of social consequences, but that's another matter).

But... One of the key features of this arrangement is that the Cleric must tap into the Source in the name of a deity. They can't call on it independently, or simply create a new deity (or force or philosophy, or whatever). And if a deity is killed or otherwise ceases to be active his Clerics no longer have the ability to tap into the Source. (The DM must take care with this - it would be hugely unfair to rule that a Cleric PC's patron deity had been killed, and thus strip the player of his hard-earned powers. But it is a plot point that came up in one older campaign, so I do want to keep it intact.)

The upshot of all of this is that excommunication doesn't exist as such in Terafa - a Cleric cannot be severed from his or her deity in the manner common to other D&D worlds.