Tell me again what happens in a game where your teammates have godmode on. What happens to challenge, story telling, "immersion"?
Always depends on the game. In Thief, you could kill (or disable) everybody without breaking the game. And then there are these games where teammates go make a nap in the middle of a battle and wake up once that's done. What do I care about these drones? They're serving a purpose, nothing else. And for those that actually have emotional involvement required, just don't make them killable. For the most part, players don't want to kill characters they feel empathy for.