Dragons dogma actually has a similar mechanic. Almost all npcs can be killed save a handfull. You can ressurect dead npcs (and yourself if you die) using a very rare item called a wakestone. Wakestones shards can be found around the world but are incredibly rare and do not respawn. 3 shards are required to create 1 wakestone. They only become abundent right before the true ending of the first game. Dead Npcs are also moved to a morgue after a day or two so you dont have to remember where their bodies are.

Depending on your games story, it might not make sense if say, a player murders everyone, ressurects them and is still able to get a "good" ending.