User blog comment:FairyRaven/Fairy Tail Chapter 324: The One Who Closes The Door, Review and Commentary/@comment-5598380-20130323001932/@comment-84.113.52.218-20130323011256

The princess said something about any human being able to use the gate, once it was unlocked earlier.

But even if any Celestial Wizard is necessary, they still got Duke Everlu and Angel in prison and might be able to buy their cooperation with a pardon... or the threat of throwing them to the dragons.