I manged to kill Janusk by accident while, building my city. I never accepted him as my adviser, and he was standing right next to me as I built a improvement in my city and I moved into his square and cut him down.
I think the game should check and if possible not move you into other NPC tiles. Maybe just place him into the city or something and have a message that says ,"XXXX has entered the city of XXX".
Speaking on the subject, could it be possible to pick the tile you come out of when you exit a city? I really don't like the random placement.
Augerman
Video of bug:
http://www.screencast.com/t/YjcxNTQzOT