>Unless, of course the rationale is that players are reborn, so
>why can't mobs be reborn.

That's how I think of it. Sometimes the NPC in question might be permanently killed through some quest. Otherwise they were merely "defeated" much like players are. The name changing thing would be a crazy thing to implement either way since you'd have to have a long list of names even for tough NPCs (other than some explore areas, there may be more killing going on than you expect).