1) Creatures do not switch to the General type DEAD when they die.
Try this again.
[edit]
Well, i tried this. They switch to 'dead' when they die. But this is reset in the next AI cycle. So, this makes the detection very difficult. You can safely detect if a weapon causes death, but it is not reliable from external scripting (because scripts don't run at every AI cycle of every creature). And totally untraceable in saved games (this actually surprised me).
2) Several effects with timing mode 9 last unto death, including glows and invisibility and scripting state changes.
This is why timing mode 9 is called permanent after death. Some effects are forcefully removed even when they are timing mode 9. Blur is an example.
3) On death the engine very likely applies some combination of ...
The creature is removed from the search map ( this is where pathfinding is calculated, doors set the impeded blocks, etc). This happens on imprisonment too.