To be honest neither in my opinion did anything to really "hurt" professional wrestling/WWE. Let's be realistic here on some factors:
Let's go back in time to Steve Austin, considering his walk out preceded CM Punk's by well over a decade. There is no denying that Steve Austin IS a legend in this business, an icon. Those two terms are obviously overused and sometimes inaccurately applied, however in Steve Austin's case no one can contest his status. Hell, I was a fan of his as "Stunning" Steve Austin and while it took a little bit of time for WWF to see that "The Ringmaster" was a complete misstep, I'm glad they came around and he reinvented himself, an obviously important move in order for Austin to have become the legend he did in professional wrestling. However by 2002 and let's be honest with ourselves here, Steve Austin's "walkout" from the WWF/E wasn't this devastating blow that some people could make it out to be. Had something like this happened during the Attitude Era, then maybe you'd have something. But Steve Austin's career was hindered by his injury in late 1999. Don't get me wrong, he did very well for himself after his return, having a classic WrestleMania main event redux with The Rock at WM X7, his time with the Alliance (although that was such a shitty angle), and his feud with Kurt Angle. However, fast forward to 2002 where he has his mini-feud with Scott Hall, and by this time, he's only less than a year away from completely hanging up the boots. WWE, much like when Hogan left the then-WWF in 1993, learned to work around not having their top guy anymore, as other stars would step up to fill the void the standard bearers leave when either moving on to another organization or dealing with a serious injury.
Now that's not me saying Austin wasn't missed during his 1999-2000 absence, but the WWF was still doing very well against WCW in continuing their reclamation of Monday Night dominance. By the time the summer of 2002 rolled around and Austin had excused himself from the promotion, the world wasn't going to end. I mean don't get me wrong, it sucked he wasn't around but things moved on. It was good to see him come back in 2003 and give himself a proper platform to have that showdown with The Rock at Mania XIX, but WWE was in no danger with any momentum loss with Austin missing.
Moving on to CM Punk, awesome competitor, I truly admire what he does in the ring, and I will say he has entertained me. However, let's keep into perspective what his place truly was in WWE. He was always going to battle someone like Cena for that top spot. I am not saying that I like Cena more than Punk because I don't. Not by one iota. I've never been a Cena aficionado. The guy's a hell of a lot better in the way of performance than any asshole smark would want to give him credit for being, but I am not part of his demographic and I just don't root for him. No animus though but just not a fan. I think Punk is the more exciting of the two to watch. But even those guys still don't hold a candle to my favorite WWE performer of the last decade, and that's The Undertaker. Obviously, he's by no means able to perform the way the aforementioned have, but all in the WWF/E of the mid-90s to late-2000s, I've always rooted for The Taker. Every single time, I digress. As awesome as Punk is and despite every great performance and his 434 day title reign as WWE Champion, he was not the guy. It was still Cena. I mean most of Punk's title defenses were the penultimate match of the event and very rarely the closing contest. Again, not saying I agree with Cena being the top guy or that I like him, but that says a lot right there.
So when Punk left earlier this year, while it definitely was unfortunate any chance of him having another run as the World Champion were dashed, it hasn't changed the swing of things in WWE, the promotion has persevered and it will continue to. Anything that hinders WWE is not indicative of who comes and goes. I believe since the Hogan/Federation era ended, they've found themselves a way to deal with every departure that occurs with the possible exception of Brock Lensar, his 2004 departure really changed the possibilities of what was to come. I think you only need to cite the rise of Bradshaw's transformation into JBL as proof of that.
As always, with threads like these, I choose to not want to speculate into the motivations of why both men "walked out" of WWE. I wasn't there, I'm just a fan who likes to watch wrestling. The business side for me is just a little too complicated and overthinking what goes go on behind the scenes undermines what being a fan should be about. I will say this one bit though, when you work in a world that doesn't believe in unionizing but yet its performers are called "independent contractors" when they are really anything but, it's safe to say that the reasons for those choosing to "walk out" or do anything that seems extreme might very well be understandable.
Oh and OP, say all you want about how you're not here to write a term paper, no one's expecting you to be a master wordsmith or linguist, but knowing the mere difference between "who's and whose" I would say is a rather important detail, an iPhone is easy enough to do that with.