The same enemies respawning again and again is something that will make an otherwise well-thought-out game world go off the rails quickly - especially if it's a post-apocalyptic hellscape.
Playing a cyperpunk game in a megaplex city with 10 million inhabitants, I can believe there is an unlimited number of street thugs hanging around (although they would stop attacking the guy who took out their last 4 predecessors - but that's another story). But thinking back to Fallout 3, there were... 30-40? npcs living in the various incredibly small settlements - and over the course of the game, I killed 400 raiders or so. And with the numbers of Deathclaws the level scaling threw at me at every fast travel location I frankly was amazed that anything else could live in an area filled with dozens and dozens of huge predators.
So please, no tilting doll enemies that get reanimated if you turn your back for a day or two.
Followup events that actually make sense would be much better - for example, if you kill a gang of raiders and leave them in a bloody pile, a mutant might have moved in and you find it chomping on the remains the next time you pass. If there was some reason why an npc was living in a location (water hole, defensive position, ...), others will be interested in that spot too - so friendly or unfriendly npcs will gravitate there - new people, not clones of the old ones - and only once or twice. A growing pile of raider skulls in front of a building _will_ keep people away pretty quickly. And a solitary big predator has a large territory - it's "neighbour" might move in if it dies, but after killing that one too, the supply of big critters for the area is depleted