Orochimaru's aint truly immortal as he can run out of chakra. Great Water Shark Bullet is not dodgeable and it will suck him of all his chakra.
Oro's rashomon might be a defense against that jutsu though. Depends whether rashomon can tank great water shark bullet. If it can, no worries, Kisame can still suck it directly with samehada.
If Oro tries to avoid direct combat because of Samehada, than water bubble and water shark dance will do. Either way Oro can't escape, he dies easily. He got nothing to counter against Kisame.
Yamata no Jutsu will just make him easy food for the great water shark so that's a no go.
Edo Tensei? Depends who he summons. If it is the four hokage, that still doesn't work as Oro would not be able to control Hashirama, which means that he and the other 3 Hokage would have to deal with Kisame and Hashirama.
At this point it can go either way, Hashirama would obviously fight against Oro to free his brother and fellow Hokage (common sense).
Zabuza and Kabuto? Could go either way, can't tell who wins this one actually. Either one could get sliced up.
I recon a stalemate would be the result. But ofcourse, if Oro retreats, cancels Edo Tensei, prepares it again (this time without Hashirama), than comes back for a rematch, than he could win. (although Hashirama, being Tobirama's bro prob knows the hand signs just like Madara, and therefore would not allow himself to be cancelled until he kills Oro, speculation but should be common sense really).
