Well, that's true Obito wanted to "teach" Naruto despair but remember, Neji doesn't really play an important role into Naruto's life other than being an friendly rival/companion/friend. Sasuke played an important role into Naruto's life as he was one of the few (Until the Chuunin Exams of course) who acknowledged him and his potential as a shinobi, no, he even at some instance, viewed Naruto as an equal in comparison to himself. Kakashi also played an important role in Naruto's life as he was one of the few people who acknowledged Naruto for his potential as well, he was actually the first member of Team 7 to acknowledge his potential at the Survival Exercise.
Sakura however, is like the "Key Factor" to Naruto's life. His obsession with Sasuke, his unyielding determination to bring Sasuke back to Konoha... He does all this just to make Sakura happy, even if he gets friendzoned in the end, he just wants the best for Sakura as he still loves her. In fact, he loves her more than anyone in the entire series. Regardless if she will love him back or not. In my opinion, I think Sakura's death is the "Key Point" to the entire Naruto series as Naruto's character development will change drastically the moment she dies right before his own eyes.
Anyhow, I wonder which character is the next one to die. Will it perhaps be Lee? Kiba? Or the Ino-Shika-Cho trio? You know, since their fathers except Choji's are all deceased. Or even better... Tenten?