Good for Cena, he's earned the time off. He's been an absolute machine, wrestling non-stop since his return from his last injury -- a herniated disk, I believe -- in November of 2008. For someone in Cena's position, that makes as many appearances, and goes through such tasking physical work -- this type of thing is unheard of. It's amazing that he hasn't hurt himself (or further hurt himself) with never taking any time off, and it's high time Cena kicked back and let his body heal, though I'm sure he'll still be making appearances for certain WWE fixtures, or maybe even filming a movie.
Cena's void will be hard to fill, but it's completely possible. CM Punk has had a huge emergence over the last 10 months, so it's definitely his time to step up and prove he can carry the show by himself. Although, Punk won't really be doing all the work on his own. Brock Lesnar is still a huge name and, as we saw on the Extreme Rules PPV, Triple H is going to be making an appearance tonight, which I'm assuming will be the first of many during Cena's (apparent) absence. The WWE won't struggle without Cena, but I think they'll definitely find out who's ready for a significant bump up the card. This is a great time for some guys to really step it up, and I can only hope they realize this and work their asses off.
It'll be interesting to see how Cena's absence plays out, or even how they choose to write him off. WWE has been hyping up an injury on their website ever since his match with Lesnar last night, but they could just as easily have Lesnar attack him tonight to solidify Cena's absence. Either way, I know I'll miss Cena's absence, and I'm sure it'll be noticeable -- though I don't think WWE will struggle with ratings, sales, or anything like that. They have plenty of talent who can work together as a unit to make this work, plus, WWE has been on an absolute roll lately, so that'll help them too.
