Not sure what NIB's policy will be - may depend on what other borrowings you have out with them. Would try to bring this down as I ran into problems years ago with BOI on this. They cancelled my overdraft. I think technically they are within their rights to do it, though it has harsh repercussions. My short answer was to entirely cease all banking with them (at the time I'd a car loan, current account and VISA card with them) as soon as everything was cleared. The irony was that when I finally cleared the VISA off they offered me a gold card (go figure that one out for yourself). I told the guy myself I'd had my current account frozen and car loan recalled and he said it didn't matter as my visa had mostly remained up to date. Crazy!
Have lived without an overdraft now for over 7 years.