Going by RAW, is there a way to (reliably) kill someone that cannot be undone? Short of outright wishing it'd never happened, I mean.
I don't mean just ImprisonmentImprisonment, or whatever. The creature has to actually be dead, and this death has to actually be non-undoable by using something like True ResurrectionTrue Resurrection.
I'm aware of quite a few in 3.5, and aware that there is a creature called a Barghest that has a 50% chance of doing this.
I'm also aware that something like this could easily be house-ruled in, but I'd prefer it if it were RAW;RAW.
Only affecting living creatures, or have obscure ways of avoiding it would be fine.
Area of effect > Single-target spell > Melee weapon
EDIT: It occurs to me that you could (possibly) transfigure an avatar of death into something, and use them to kill someone. I'd be cool if there was an answer derived from this, as long as it's RAW.