[unkala]

If you want the NPC to respawn instantly, add the "<NPC> deactives" and then the "<NPC> activates" actions, in that order, to the NPC's death event. Add the conditional "<Scenery Object Interaction X> has not triggered" so the respawn only happens if no one has interacted with your object yet.

This is rather abrupt, though, so you'll probably want a short timer. Make the NPC's death start the timer, again making it conditional on the object not being used yet. Put the deactivation/reactivation on the timer trigger event.

(The reason for deactivating the NPC is to get rid of the corpse. A mob is still active while its corpse is on the ground, and trying to activate an active mob does nothing. Corpses take over a minute to vanish naturally. If you're always going to wait longer than that to respawn, you won't need to do an early manual deactivation.)