Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Yes, it's important to consider what threats would rise if Mega Sableye left. There's a lot of powerful mega fighting types out there, and Mega Sableye helped keep them from overrunning OU. With Mega Sableye gone, the metagame could very easily be a lot worse. Besides, Mega Sableye isn't even...