If the IRS has not made any recent changes to their way of allowing tax payers to provide updated information to new bank accounts wherever new changes arise, without having to gather that information on the next year's tax forms, then the only thing that will happen, is that your direct deposit to your old bank account will get rejected by that bank and the direct deposit returned to the IRS.
However, when this happens, the IRS will then issue you a paper check to the last known address in their files. Hopefully, you haven't moved to another address since you completed your 2019 taxes.
