Some NXT talent is ready for the main roster. As soon as Kassius Ohno is toned up enough to WWE's satisfaction, I'm sure he'll be on the main roster soon. Paige is someone that, in my opinion, is ready for the main roster. She's officially been 21 years old for the last 3 weeks and while that's extremely young, she's also someone that's very much grown up in the business. I'm sure there are others who are ready, those are the two who immediately sprung into my head first.
As far as all the various injuries go, it's the nature of the beast that is pro wrestling. More often than not, wrestlers are usually working injured or hurt to one degree or another. I don't believe that there's any major detriment to WWE right now as far as star power goes. CM Punk & Daniel Bryan are both insanely over at the moment, the corporate power structure is garnering tremendous heat, as are The Shield for being the physical enforcers of the power players' collective will, babyfaces who have felt their wrath like Big Show, Dolph Ziggler & Cody Rhodes have fans rallying behind them, things look to be picking back up in the tag team picture and, hell, even the Divas are fairly relevant these days. John Cena being out injured is a blow because he's a significant money player for WWE. It's always shitty for a company when someone like that is on the shelf but, as I alluded to earlier, that's how the mop flops in wrestling.
The main roster isn't in any trouble that I can see thus far but even there was, I doubt WWE would improve things by rushing a bunch from NXT to the main roster before they're ready. The law of averages suggest that there'd be a substantial number of those put on the roster so quickly wouldn't be ready.