I've been reading a lot of threads where people are wondering what Gai sensei, sakura etc are doing. So to clear up Gai's whereabouts to you I've highlighted where he is in Manga Chapter 617.
Looks to me like Gai is taking charge with Naruto and Lee.
Here we see there is only one person with the Lee/Gai haircut and the action shows that Gai has pushed/thrown something towards Madara. That something being Lee We also see Kakashi has joined in on the charge in this panel!
Let me know what you think! Sorry if this was super obvious to some of you, but it was getting annoying seeing people commenting about how Lee couldn't have been fast enough to kill Madara before he took up a defensive, and where the hell is GAI?!