Kill all the cannibals will i lose all those merchants? I mean, will anyone take the women's place on the shop? Will the horse seller also allow me to buy Vigilanti? I'm ok with losing the meat seller, bastard was really annoying anyway, but i'm more worried about the rest...

When I killed them, there is a man who attends to the store.

The man at the stables selling horses is still there. I am sure that the one you killed just sells the fighting dogs.

Hm... ok, good to know someone else will tend to the store, as for the rest... oh well, i have Meeko, so i guess i won't mind not being able to buy vigilanti.

I suppose if you really want to buy him, you can reload an earlier save, and then use the dog to kill his former trainer (I think the irony would be great )

Lisbet's employee will take over Arnleif and Sons, though he will treat you shabbily. How he knows of what you did is anybody's guess. The meat vendor never gets replaced, but those vendors are useless anyway. You'd think the bum or even Hroki would take over the stand, considering how much time they spend there.

Like he vaguely lets on in his interactions, the meat seller at Windhelm is more a jack-of-all-trades when you try to barter with him. He's been a great help to me up to now. But you're probably right about all the other meat vendors.