My take on how that works is that it's actually a flow of magical/life-force energy.. & not just a finite amount of bottled up energy in a human vessel.. So when she's draining their magic/energy power from them, she's pulling it faster than they can regenerate it, or pull it from the source for themselves..All that to say is I think wiccans power will recharge over time.. Either that or I am also a huge fan of all of the stolen powers returning to the rightful owner when the magick thief dies