Is it possible to complete a playthrough of the game without killing a single character?
Yes, we're aiming for that. It's a big development task, but it was one of the design goals right from the start. It might be necessary to rely on stealth for a lot of situations, but we want to include more tools for the player, too.
Similarly, is it possible to, through your actions, get every NPC in the game killed, regardless of their importance to the story?
Yes, that will be possible, too. I'm not sure at this point if we can guarantee the world will still give enough hints and clues to pick up the story after killing a very important NPC, but at the very least it will still be possible to mechanically reach the end.
How hard is it to balance that feeling of freedom against making sure it doesn't totally ruin the game's balance?
I'm still figuring this out. It's my first game in this genre so there's not much personal experience I can reuse apart from my knowledge as a player and my research. It looks like it's indeed a lot of work and also more about finding good compromises instead of looking for perfect solutions. I would always favour freedom over balance though and then give tools to the player so she/he can customize that balance again so the game has a good flow but also doesn't get too easy.
[...]
