Off the top of my head it's the most reliable to patch .cre effs with a delayed (value 2 seconds) item removal effect rather than having the item removed via scripting.
That may be a reliable way of getting rid of the item, but it's not a reliable way of making sure the correct script runs. Unkillable, relentless undead may be unfortunate, but at least I can be reasonably sure to get bug reports. (And the current approach is not susceptible to having other scripts interfere.)