[X] Investigate the TAs, getting them to retract the permission. As a teacher, when this sort of things happened, students should have come to you and not the TAs. You knew that TAs were given many responsibilities to better prepare them for the future. You were quite sure that they shouldn't have this much power though. Plus, Zon didn't seem the type to overlook you.
[X] Tell Tycho about this development. As a teacher, it was your duty to make sure that your students are sufficiently prepared for all kinds of troubles and obstacles life threw their way. You felt obligated to tell Tycho about the upcoming fight so that he can better prepared himself.
[X] Convince Zon to rescind the challenge. As a teacher, you valued students cooperation and harmony above all else. In fighting between classmates will dissolve class unity. You didn't want that to happen simply because you were their teacher. You wanted Zon to not act too eagerly about this.