I'm willing to bet said episode is one of the many instances that fuel our hatred for Diamond Tiara. While most AU fics pertaining to this episode involve the crusaders running away, what if instead of that, they decided to "confront the problem head-on"? I originally wrote this in the Ponyville Confidential call-out group, but here's something I think would make for a satisfactory story:

Nopony will listen to the CMC or give them the benefit of the doubt. Having been yelled at, shunned, and treated like dirt by everypony in Ponyville, they succumb to their inner demons. Feeling they had nothing left to lose, and that it was Diamond Tiara's fault for the current situation they were in, they decided to make her pay. They go back to the schoolhouse basement and confront Diamond Tiara. They choose to tell her one more time they quit, but she refused to accept their resignation and reminded them of the picture she had of them. With that, one of the Crusaders pushed her out of the seat onto the floor and they surrounded her. Diamond Tiara (now worried) would start threatening the Crusaders by telling them they'd get in deep trouble if they did anything to her, but they didn't care. They then started pounding Diamond Tiara into the floor. Apple Bloom being the strongest would hoof punch her mercilessly calling out all the harassment she and her friends had to endure at her hoofs. Sweetie Belle would use her magic to restrain Diamond Tiara so that she couldn't move or escape. Scootaloo would make sure nopony intervened or tried to stop them and would taunt Diamond Tiara like she used to taunt them. This would go on for a long time, Diamond Tiara would desperately plead for mercy as her once pristine body was relentlessly pummeled by the powerful earth pony hoof strikes. Eventually, they would stop, leaving Diamond Tiara a bruised and bloodied mess, she was in so much pain that even after Sweetie Belle lifted the restraints she couldn't move. As one final definitive act of revenge, they would take her tiara and throw it into the printing press, destroying both in the process. Gabby Gums was finally over. The Crusaders wouldn't care what consequences would follow for them, all that mattered to them was Diamond Tiara finally got her just desserts.

7770416 You know... there's no crime if there is no body. CMC could get away with it, they'd just have to make sure that no victim is found, if you get my drift.