Actually I already explained why I think Deidara wouldn't be there, I think you should read that and his personality has alot to do with it. I don't think the Akatsuki members are always together, they all have their own goals and they just work together to complete their mission objectives. Sasori was obviously doing this without Akatsuki's knowledge, I don't think they knew about him having spies in the Sand either, well ofcourse they did but not because he told them but because he was from the village. The Akatsuki operate independent of each other they just come together to capture and extract the Bijuu because that is part of some common goal.
Secondly Sasori wasn't going to be expecting Orochimaru to be there because he certainly didn't know that Oro had broken his hold on Kabuto. I don't think he was expecting anyone in the sand village to break his jutsu so he of course wasn't expecting anyone else to show up when he went there. He also didn't help Deidara at all during that mission he just got him into the village it was all him after that. Akatsuki don't help each other or care if each other dies, they are villains remember so I'm guessing if you aren't strong enough to defend yourself then they won't care about you. They certainly didn't care that Sasori had died.
Thirdly I don't think it would have mattered if Deidara was there because Oro should easily have been able to deal with Sasori and Deidara by himself. We've seen all of Sasori tricks and he most certainly should have known them since he had already seen Sasori's real body. Kabuto would have destroyed his puppet with his first attack and then it would be easy for them attack his one weak spot. Oro's goal is to learn every single jutsu in existence so there is no way Sasori would know all his tricks since I assume he is constantly learning new techniques. That is why he said he was thankful for Kabuto in the first place since he helps him with his experiments. Sasori's main weapon was poison and I highly doubt that would've worked on Oro and his other jutsu's weren't anything too difficult to deal with. I mean he did get beat by Sakura and an old woman.
He wanted to know the secrets of Orochimaru's transfer jutsu so he could kill him, Akatsuki is supposed to be hunting him down so they could kill him because he left the organization. So knowing how his jutsu works is of the utmost importance because it would be futile to try and kill him if you know that he had learned an immortality jutsu but you don't know its limitations.
And yes Deidara and most of the other ninjas should easily be able to over power Kabuto. Hell naruto did it in part one but Kabuto is a medical ninja power isn't his strength. His strength is skill and analytical ability together with his knowledge of jutsu and his regeneration abilities that is what makes him difficult to deal with.