That’s an interesting possibility, but I favour the interpretation that this is the source of dementors:
Even so, the most terrible ritual known to me demands only a rope which has hanged a man and a sword which has slain a woman; and that for a ritual which promised to summon Death itself—though what is truly meant by that I do not know and do not care to discover, since it was also said that the counterspell to dismiss Death had been lost.
Canon makes reference to fog being produced by dementors breeding, which doesn’t sound like a light ritual or a respawning option. I don’t know if Yudkowsky has kept this part.
That’s an interesting possibility, but I favour the interpretation that this is the source of dementors:
It fits very nicely. Dementors (Death) were unkillable (undismissable) because the “true” patronus charm (counterspell) had been lost.
Canon makes reference to fog being produced by dementors breeding, which doesn’t sound like a light ritual or a respawning option. I don’t know if Yudkowsky has kept this part.