By that point, there were the first scenes of the lab (that ended up overused by Inoue and co, killing the mystery of the figures) and Asumu's growth was obvious... even though he wasn't succeeding in his attempt to get into that music school group.
From the Makamou/Oni side, I guess it'd eventually lead to some new type of Makamou, requiring help from the minor Onis in some battle (many had suits done but even so didn't appear in the series). There were many comments through the first part of the series about the experiments and evolution of the Hime/Doujis. The final enemy probably would have been a new creation, rather than a menace from the past.
For Asumu, I'm pretty sure he wouldn't have his characterization regressed due to the arrival of some "rival". I'm not sure he'd have become an Oni though, but I'm pretty sure that if he did become Hibiki's official disciple at some point, he wouldn't just walk away afterwards.
Akira's character also was completely derailed by the new staff. Suddenly, she became utterly incompetent and lost any will to become an Oni after meeting a corrupt Oni... There's no way that would have been in the original plans. The Shuki arc doesn't fit in at all with Hibiki information given in Hibiki's first half, especially her relation to Zanki, so it wouldn't even exist. I'm not sure about Asumu, but I'm certain Akira would have become an Oni.