I hope... But ya never know. It shouldn't even be joked upon though cause it's not really funny... If he was joking I feel he would have done something like you did:
AFKing at a Wither cobble-gen won't kill the market people can mine it themselves almost as fast. If you can make a wither, you can get a star, and make a Haste Beacon
Perhaps I will build one to demonstrate, then tear it down. "Why tear it down?" you say. Because it's dangerous (Unless built away from civilization), and inefficient on time/resource (compared to high efficiency smooth stone generator, or Beacon Mining). I do believe this would be much better built somewhere else with access to bedrock in a better formation. And on the EMC server, the customization makes this even better. Being a multiplayer server, with no grief protection, it would be easy for someone to intentionally/accidentally release the wither and destroy everything nearby, including peoples builds. It would be a nightmare. Anyway, just my thoughts. Cheers Scruffy