The best way to interpret how the central conflict was resolved in the story is: The central conflict does not have a resolution with this ending, but rather ends in an ironic way.
This interpretation highlights that while the initial conflict of breaking the window is addressed through the decision to leave a note, the ultimate outcome involving the tornado introduces an ironic twist. The resolution of their conflict becomes overshadowed by the dramatic event, which renders the girls' concerns about the broken window relatively insignificant in the grand scheme of things.