What I think is that oro did manage to survive the totsuka blade via his snakes, like sasuke said, oro is a resiliant madda****a, not a direct quote.
The problem with the curse marks is that its not the same as Minato sealing his chakra in naruto. I think kishi showed anko's curse mark as a way for sasuke to figure out that oro is still alive. If you remember, when danzo died his curse mark on the root people went away, yet anko's is still there, so that is a way to show that oro is still alive and kicking.
The curse mark is only good for an indicator and power up, which is why anko is still alive, as oro's chakra in anko regenerates Kabuto sucks it up, thats one reason why he is so strong and how he became so much like oro.