Given that, despite all the customer frustration that exists right now, they haven't been losing customers. I don't think that Chip+PIN failing to work correctly at first would cause customers to switch. Chip+PIN cards would only be cycled into use gradually, as people replaced their older, swipe-only cards with Chip+PIN cards, or signed up for new accounts. There would be more than enough time to sort out any problems, and you could also start out by making Chip+PIN optional for new/replaced cards.