Kabuto won't change into Orochimaru
Kabuto: But part of me is doing everything it can to resist being taken over!
Kabuto: I can truly sense that part of me that strives to surpass Orochimaru-sama!
Kabuto: After I become completely able to control Orochimaru sama's power, I'll return to fight you Naruto-kun. But you'll be my second target. First I'll exact revenge on Orochimaru sama's murderer, Sasuke-kun!
Conclusion: There is no way Orochimaru will reincarnate into Kabuto. Besides, Orochimaru's spirit is trapped within Sasuke (giving him the white snake recovering ability), not Kabuto.
If Orochimaru was to ever return, he would thro Sasuke's body.
Kabuto is now a villain on a totally new level, the final villain.