(I will not be talking about David lee and Danilo Gallinari today)
Last season, and even in the playoffs, the NBA had some injuries pertaining to stars. Derrick Rose, Kobe Bryant, and Rajon Rondo had 3 torn or hurt ACL's (Technically Derrick's was from the 2012's playoffs). Kevin Love had a broken hand, and Russell Westbrook had a meniscus tear in the 2013 playoffs. All of these looked pretty painful and ended up costing their teams.
The Bulls just weren't the same without Rose. They were knocked out in blow out fashion, in the second round of the playoffs. The Lakers were struggling all season anyways, but with Kobe gone, it just got worse. The Lakers were swept in the first round of the playoffs by the future Western Conference Champions. Boston actually didn't have a major downfall from Rondo's injury, but they were still knocked out of the first round of the playoffs. The Wolves didn't even come close to making the playoffs, with Rubio being their best player. Finally, the Thunder went from being Western Conference Champions to being knocked out in the second round without Westbrook.
If you look at the impact stand point from last season, you have to go with Rose or Westbrook. Rose led the Bulls to the best record in the NBA when he was healthy, but the Bulls fell to the 11th best record without Rose. Their defense was the same, but their offense was the second worst offense in the NBA. The Thunder were Western Conference Champions with Westbrook, but second round losers without. The Thunder were up 2-0 in the playoffs with Westbrook, but fell to 3-6 without.
The others? Kobe was part of the problem in LA, so him leaving didn't affect them too much. The Celtics had a better record with Rondo during the regular season, than without. They were 20-24 with, and 21-16 without! However, they did struggle to find ways to beat the Knicks in the playoffs without him. The Wolves ended up the 12th best team in the East, with or without him.
Now the real challenge is figuring out, who will have the biggest impact next season. Well, first off, Westbrook and Rose are going to have huge impacts for their teams. We have proof from last season! Love will probably have the smallest impact, because his team is poor with or without him (Although they may be better with the new addition: Kevin Martin).
This leaves Rondo and Kobe. Rondo has lost 2 of his best players during the off-season, and therefore will need to have a huge impact. He still has Jeff Green, but that's really it besides Brandon Bass. Kobe, on the other hand, only lost Dwight Howard. In all honesty, the Lakers did better without Dwight. The Lakers were 3rd in the west without Howard, but 7th with. Besides, Kobe has Pau Gasol and Steve Nash still. He'll be fine. Rondo only has Jeff Green, who is no where near Gasol. Rondo will definitely need to have a bigger impact than Kobe.
Now, its between Rondo, Westbrook, and Rose. Well, Westbrook still has Kevin Durant, Serge Ibaka, and Scott Brooks. The Thunder were still a good team with Westbrook. However, they were not title contenders with Russell. He will need to have an impact, but an impact like Rondo.
The Bulls were also a good team without Rose, but are not a title contender without Rose. Rose has Joakim Noah, Luol Deng, and Carlos Boozer. Again, he needs to have an impact, but no where near Rondo's.
If the Celtics are to be a title contender, or even a good team this year, Rondo will have to have the biggest impact out of all the injured stars.