The immortality essentially makes it a stalemate unless Aizen resorted to would burial. All in all Aizen then soley because of that.
With Oz out of the picture I think they could do it. Outside Moria, who they could gang up on and defeat overall, Ryuma is probably the biggest threat. Kaku might be able to beat him with extreme effort but that is pushing it. But Lucci could. Absalom and Hogback would be easy. Perona's ability is tricky but could likely be overcome with speed, which all CP9 have. In short, I'd say they could do it.