Orochimaru has no way to hit Minato, too slow for him. One touch and he becomes Minato's property. One touch with the contract seal and he loses his summoning capacity which is Orochimaru's main fighting style besides Kusanagi(something he seemingly lost after Itachi sealed him with totsuka). I'm not sure if Orochimaru can survive decapitation. If he can't, he loses the moment Minato cut his head if he realises he can't kill him another way.
If he can, it will become a battle of stamina. Problem is that to survive, Orochimaru uses a high level of kawarimi no jutsu which is stated by Itachi to take too much chakra, so all Minato would have to do is to continue to kill him until he can't use the jutsu anymore(not sure if Orochimaru can use it more than 5times anyway, but this is just my assumption based on Itachi's statement). If Minato gets bored, he uses his summons(with sealing barriers) to capture Orochimaru there with the flying thunder god technique for eternity, or uses his eight trigrams sealing technique to seal Orochimaru completely in an object after making the preparations