Can’t close my Japan Post Bank account before leaving the country, what will happen ?

In Japan for a study exchange, and had problems with my credit card when arriving, so I opened an account with the help of the uni in panic, but never received a credit card or bankbook, and since I solved my credit card problem, didn't pay any mind.

I know I'm supposed to close the account before leaving the country, but you need either the credit card or the bankbook, but I can't reissue them in time (especially since it's only for closing an account…). So what will happen? Do I just leave the country and they will freeze+close my account ?

by Ink-ami