I work for Nike and there was NEVER any discussion other than to pull the plug once he was indicted. And even this has huge, detailed legal complexities involved; its not just as easy as saying no go.
No backlash, Vick's been banned from camp by the NFLI love saying "I told you so." Seriously, I don't see where Nike had a choice in this matter. Wait for the backlash that comes when the Falcons open camp.