Definitely Naruto. He's always been there for Sakura, no matter what. He would use his Nine - Tails chakra if he had to in order to save her. Sakura's female friends like Ino could also play a role in her rescue. Ino is a skilled ninja in her own right and has a deep friendship with Sakura. And don't forget Tsunade. As the Fifth Hokage and Sakura's mentor in the medical field, she would do everything she could to save Sakura's life.
Well, first off, Naruto. His loyalty to Sakura is unwavering. He'd fight tooth and nail to save her. Then there's Rock Lee. He has always admired Sakura from afar and would surely jump at the chance to rescue her. Also, Shizune, Tsunade's assistant. She has medical knowledge and combat skills. If Tsunade couldn't be there immediately, Shizune would step in to try and keep Sakura alive until more help arrives.