Actually I think it's mapping, isn't it?
Anyway, zu must give the NPC this:
KEY: NPC_target
VALUE: 1
KEY: targetname
VALUE: 1
KEY: delay
VALUE: *time till the NPCs respawns in seconds*
Then you have to create an Trigger_always and connect it to a target_relay wich is connected to the NPC.
The target_relay must be:
KEY: wait
VALUE: -1
