Nope. They just ignore your blows entirely.
They don’t turn hostile in the first place.
Nope.
Until fairly recently, you could do all of the above to Vathis the Hierophant (he was not a talking NPC then), and he’d respawn after ~15 minutes (same timer as anyone else). He could also respawn in a female version. A few patches ago (or last patch, if you don’t count the hotfixes), he was turned into a talking NPC that could no longer be attacked or tamed.
Ordinary denizens of Sepermeru (Fighers, Archers, and the various crafters) can be attacked and enslaved as normal (as you know). I don’t know how long until they turn non-hostile again, as I always just kill 'em. Merchants count as story NPCs and can’t be killed IIRC (been a while since I tried that though). Last I tried you could knock them down/out, but they’d continue talking to you (selling you stuff). You can’t enslave them though.
The victim and anyone standing next to them I believe - the “aggro range” is tiny though.