Anyone who claims to know that Big Al is done after watching him this season is mistaken. Yea he is having a bad year, most high level NBA players who come back from a major ACL surgery do. People didn't even expect him to play until December or January, he was on the court in September. He might get traded because of fit or whatever but in no way can anyone say that the guy is done. For many players it takes over a year to get back from something like that.
You don't just miss game time, you lose strength, timing, conditioning, everything. Players who play at an elite level are SO fine tuned into what they do that the slightest change can completely throw them off. That's a reason why so many top athletes have trouble producing when they get in their 30's. They lose just a little bit of speed, quickness, or explosiveness and it completely throws them off.
Look at this quote from Nuggets strength and condition coach.
http://www.seattlepi.com/basketball/309644_nban30.html
"You have to take into account the size of these guys, I'm telling you it's different," said Hess, who helped Nene work off 20 pounds during the season. "When you are 7-feet, 270 pounds, the force on that joint is a lot different than a guy 5-feet. The specific area is a hot spot for up to two years, and it definitely takes between 12 and 18 months to come back. And you want to take your time because you want to be the best you ever were when you come back."
Amare had a serious injury and he had to sit out the season and come back in 06-07. Oden had one in 07 and didn't start to look like an NBA player until 2009. You wont see the real Al Jefferson until next year. It's a bit pre-mature to say the guy is done and will never be the same. If Al Jefferson is playing like poorly this time next season, then I may buy into the "he will never be good again" hype but until then, I'm not worried about him regaining his form.