Botted 24/7 for like 6 months on 3 accounts and still got all of them. My "main" bot account has 250+ days played and is not banned yet my main account however got banned in December 2012 after botting for roughly 30 hours over the course of a week.
Just the CD key, yeah. And you can buy a new CD key and add it to the same battle.net account and start playing/botting again like nothing happened. When my main account on the same battle.net as all my WoW accounts+SC2 account etc got banned I just bought a new one and botted a new char to plvl 100 straight after. I wasn't banned again after that.