Hogan leaving and signing to WCW. That will probably always remain one of the biggest, if not the biggest, the same would be said if Cena did the same, left and moved on to TNA (though very unlikely) the news would be a lot bigger.
This has been a crazy week though, dirt-sheets are having a frenzy, kind of fun to watch honestly.
I don't think the Hogan thing was that big a deal at the time. Sure, it gave WCW an added piece of credibility, but they were so far behind at that point that I doubt the WWE really thought it would be the turning point for the competition. Even watching the Hogan parade on TV as a fan, I got the impression that it was second rate. Sure, I'd tune in from time to time to see what was going on with Hogan, but it never once titled my allegiance from WWE programming. I can't say for sure that the WWE felt that way, but by 1993, they'd really milked the Hulkamania thing to death - even his loyal fans were starting to turn on him - and he was 40 years old.
Obviously, the WWE was wrong on this one ... but it took the deflections of Scott Hall and Kevin Nash a few years later to prove that fact. To me, that moment was much more damaging to the WWE than Hogan because WCW was, if nothing else, viable competition to the WWE by that point. To take two of the WWE's biggest stars at a time when they were running neck and neck likely caused a few more sleepless nights for Vince McMahon than losing Hogan did.
Now, while a lot of people are pointing out the MSJ from November 1997, I think they're forgetting an equally - if not more - disastrous situation from just 9 months earlier. We like to laugh about Shawn Michaels losing his smile. Hell, the OP even referenced it as a comical means to describe CM Punk in the thread starter. But do we really grasp what that situation meant to the WWE at that time?
This was a time when the WWE was getting destroyed by WCW. The company was a few more lost viewers from possibly folding. They were desperate, and they needed WrestleMania 13 to be a huge success. Fortunately, they had an ace up their sleeve. They'd planted the seeds for an HBK/Hart re-match during the previous year's WrestleMania. There was a ton of fan interest from this re-match, and the WWE planned to milk that by making people wait a full year for it. And then what happened? Their champ, the guy carrying their company, forfeited the belt and walked out on the company because he 'lost his smile.'
So six weeks out from a match the company had been building for a year, at a time when they legitimately feared they might go out of business, their biggest star left the company.
Now, there's no question that the fans' resentment of the product due to the perceived slights of Daniel Bryan coupled with CM Punk's departure are tough blows. It has absolutely been a crazy couple weeks for the company, but they'll survive this. There's no competition and w/ the network ready to launch and a new TV in the works, that company is just printing money.
Additionally, I don't buy that Punk is "gone." I'm not saying what happened this past Monday was a work, but I struggle to believe any wrestler is ever truly "gone" from the company. With no real viable options, Punk is likely to return to the company once his body heals, he gets his head back on straight, and that itch to perform in front of live audiences returns. I can't say when that will be, but it will happen. Top stars never leave for good at 35.
And as for Daniel Bryan. He's likely to benefit from this. Someone on another thread came up with an idea of adding a stipulation to the Daniel Bryan v. Triple H match at WrestleMania. If Bryan wins, then the main event is a triple-threat match. This would allow a number of things to happen. 1) Bryan would end the show with the title and the crowd chanting YES. 2) Bryan has faced two obstacles since Summerslam (Triple H and Orton). This would allow him to overcome both in one night. 3) The crowd would go crazy as Bryan would likely be in the ring for an hour of the show.