I don't agree that gymnasts who have competed and done well in an olympics or other major competition should just hang up their leotard and be done and let someone else "have a chance." I think gymnasts should compete as long as they want to, and as long as they can. I think the best gymnasts should shine, not just the newest gymnast, or the gymnast that the US media want to turn into the next big thing.
Nastia can still get back to her previous top form, and she's really not that far off if you look at her beam routine. She just hasn't had a chance to do the numbers, which is what brings consistency. If she gets back to her previous form, and is the best... why should she stop competing just so someone else has a better chance of winning with her out of the way? I applaud Nastia for sticking with it (and any gymnast who keeps competing for a long time!) and seeing how much she can do, and potentially seeing if she can win more medals.
And why not? These girls shouldn't be competing in gymnastics for the sake of getting famous, and then quitting when they do. They should be competing to be the best gymnast they can be, or to see if they can be the best gymnast in the world. Oksana Chusovitina has competed at the elite level since 1992. Beth Tweddle (while I'm not her biggest fan...) is shooting for the 2012 olympics last I heard. Anna Pavlova competed in 2 olympics as well. The best gymnasts are the ones who aren't just a flash in the pan, but who keep coming back, and who keep being the best. Look at Nadia Comaneci, who was a sensation after the 76 olympics... she came back in 1980 to win gold medals. Should she have quit so that someone else could get a chance to win gold?
I think the US media has been hurting gymnastics as of late, by making it a popularity contest. They're so quick to latch onto celebrity, and I think it detracts from the sport and the athletes and what they do. Everyone says that the publicity is good for the sport, but I think it's the wrong kind of publicity. It damages these girls' gymnastics careers, it doesn't help them. If there hadn't been all the media appearances and hype, the girls could have just gone right back into the gym, which is what most athletes from other countries did after the olympics.
I'm sorry for this long rant... I know it's kind of unrelated to whether Shawn Johnson in particular is coming back.