4. That has been in the games since Gothic1 i believe, it's in Gothic2,3 and Risen at least. You can't kill all characters in this game either, some will auto restore their health. Usually you can knock them out and you can loot them, but they will wake up.
This is attention to details that seem so much important
1. There are no stealth kills in gothic games, never were and probably not in r2. Codexers correct me if I am wrong. In all gothic games NPCs do react to weapon being withdrawn even when you're standing behind their back.
2. G1/G2 had exactly same critical NPC division - their health won't decrease at all no matter how you try. All other NPCs work more or less like this - you knock them down to almost zero hp and then you can loot their body another great thing strangely missing in r2. At this time you can kill NPC with devastating effect on your local reputation (of course if anyone sees you), otherwise NPC will slowly stand up and then it will have almost zero hp and thus may decide to eat some food which will eventually increase its hp. Just think how simple, good looking and plainly well done this is done. Sacrificing such stuff is a crime IMHO